3.5. Colors

This section contains information about using colors in PHPlot. Functions described in Section 6.3, “Colors and Line Styles” in the Reference chapter control the use of colors in PHPlot.

This section describes Palette images. Starting with PHPlot-5.1.1, a second color model is available in PHPlot: Truecolor images. Refer to Section 4.3, “Truecolor Images” for more information.

3.5.1. Color Parameter Forms

Individual colors as arguments to PHPlot functions can take one of the following forms:

  1. A color name, as defined by SetRGBArray or from a built-in color map if SetRGBArray was not called. Note that color names are case sensitive.

  2. Numeric color component values, in the form #rrggbb. Here rr is red, gg is green, and bb is blue, and each component value is represented as a 2-digit hexadecimal number between 00 and ff. For example, #0000ff is full-saturation blue.

  3. A PHP array of red, green, and blue color component values, each value being in the range 0 to 255 inclusive, for example array(0,0,255) for blue.

Additional color forms can be found in Section 4.3.4, “Color Parameter Form Extensions”. Those forms are more useful with truecolor images.


You cannot use the (red, green, blue) array form as a color value in those functions (like SetDataColors) which accept either a single color or an array of colors. The functions are unable to distinguish between an array of colors and a single color represented as an array. However, you can work around this restriction by using an array containing the array with the colors, for example: array(array(102, 0, 192)).

3.5.2. Built-in Color Maps

There are 36 colors defined in the 'small' internal color map. This is the set of color names which are available by default, unless SetRGBArray is used to load in a different color map. The colors and their names are shown in the figure below.

The 36 color 'small' color map

Here are the color names again.


The color names and values in the 'small' internal color map are selected from the X11 RGB Color Database. If you use SetRGBArray to pick the 'large' color map, PHPlot loads a much larger list of colors equivalent to the entire X11 RGB Color Database. Note that there are some duplicate colors in the maps, as they include alternate spellings (like 'gray' and 'grey').


You are not limited to only using colors from the color map. The color map contains a list of color names that PHPlot can translate into color values, but you can use any color at all by specifying the color value using one of the numeric representations described above.

3.5.3. Plotting Colors

Each data set plotted on a graph uses the next color in the Data Colors list. By default, the Data Colors list contains the following 16 colors in order.

Data Set:Color Name:Color Sample:

An additional color list is used with error plots. These have data type data-data-error or data-data-yx-error (see Section 3.3.1, “Available Data Types”). The positive and negative error bars use a color map that is set using SetErrorBarColors. By default, this color list contains the same colors as the data color list, so each data set and its error bars will be in the same color. If you change the data colors list with SetDataColors, you probably want to change the error bar color list too, so you get the same colors for data sets and their error bars.

Some plot types support data borders, which are outlines around filled areas. This includes the bars and squaredarea plot types, for example. Use SetDrawDataBorders to enable or disable drawing of data borders. The colors used for data borders can be set with SetDataBorderColors. By default, a black data border is used for all data sets, if borders are enabled.

Note: PHPlot through version 5.0.7 used 8 colors in the default Data Colors list: SkyBlue, green, orange, blue, orange, red, violet, and azure1. If plotting more than four data sets with PHPlot-5.0.7 or earlier, you should use SetDataColors to define your own data colors list. Otherwise you will get two data sets plotted in the same color, orange.

Instead of using sequential data colors for plotted data sets, you can control exactly which data color is used for each data value using the data color callback. For more information, see Section 4.5, “Custom Data Color Selection”.

Some plot types which only support a single data set still use multiple data colors, but in a way that is specific to that plot type. This is described for each applicable plot type in Section 3.4, “PHPlot Plot Types”. For example, the 3 OHLC financial plot types use the first 4 data colors for different parts of the marker at each data point, as well as to indicate the overall direction (up or down). You can use the same methods - SetDataColors or a data color callback - to change colors for these plot types.

3.5.4. Transparency

You can designate one color in the color map to be transparent. This is most often used to make a plot with a transparent background. Use SetTransparentColor to designate the color, and SetBackgroundColor to use that color for the background. Use a color which is not otherwise used in the plot.

For transparency to work, the output format (see SetFileFormat) must support transparency, and the the user's viewer or browser also must support transparency. If transparency is not supported, the user will see the actual color which was designated as transparent (so don't use red, for example). Most viewers support transparency in GIF format, and newer viewers should support transparency in PNG format. JPEG format does not support transparency.

3.5.5. Plot Element Colors

The following table shows the function(s) used to set the color of each element on a plot, and the default color if no functions are used to change it. Where multiple function names are shown, they are listed from highest to lowest priority. (That is, if the first function is not used, the color is set with the second function, etc.)

Plot element:Function(s) used to set color:Default color:
Data bordersSetDataBorderColorsblack
Data elements (points, lines, area fill, etc.)SetDataColorsSee Section 3.5.3, “Plotting Colors”
Data value labelsSetDataValueLabelColor, SetDataLabelColor, SetTextColorblack
Error barsSetErrorBarColorsSame as data colors. See Section 3.5.3, “Plotting Colors”
Image backgroundSetBackgroundColorwhite
Image borderSetImageBorderColor#c2c2c2 gray
Legend backgroundSetLegendBgColor, SetBackgroundColorwhite
Legend color box fill or shape markerSetDataColorsN/A
Legend color box bordersSetTextColor or SetDataBorderColors (see notes)black
Legend borderSetGridColorblack
Legend textSetLegendTextColor, SetTextColorblack
Main titleSetTitleColorblack
Pie chart data labelsSetPieLabelColor, SetGridColorblack
Pie segment bordersSetPieBorderColor, SetGridColorblack
Pie segment fillSetDataColorsN/A
Plot area backgroundSetPlotBgColorwhite, but disabled by default
Plot borderSetGridColorblack
X axis lineSetGridColorblack
X axis data labelsSetDataLabelColor, SetTextColorblack
X data label linesSetLightGridColorgray
X grid linesSetLightGridColorgray
X tick labelsSetTickLabelColor, SetTextColorblack
X tick marksSetTickColorblack
X titleSetXTitleColor, SetTitleColorblack
Y axis linesSetGridColorblack
Y axis data labelsSetDataLabelColor, SetTextColorblack
Y data label linesSetLightGridColorgray
Y grid linesSetLightGridColorgray
Y tick labelsSetTickLabelColor, SetTextColorblack
Y tick marksSetTickColorblack
Y titleSetYTitleColor, SetTitleColorblack

The following notes apply to the table of plot element colors above:

  • Data borders refers to the borders, or outlines, around bars in a bars or stackedbars plot. Data borders are also available with the area, squaredarea, stackedarea, and stackedsquaredarea plot types.

  • SetPieBorderColor was added in PHPlot-6.0.0. In prior releases, pie segment borders (which were available only on unshaded pie charts) used the color set with SetGridColor. The new function is backwards compatible, as the borders default to the grid color if SetPieBorderColor is not used.

  • SetDataLabelColor, SetDataValueLabelColor, SetPieLabelColor, and SetTickLabelColor were added in PHPlot-5.7.0. Through PHPlot-5.6.0:

    • Tick labels and axis data labels all used the color set with SetTextColor.

    • Data value labels (incorrectly) used the title color set with SetTitleColor.

    • Pie chart labels used the grid color set with SetGridColor.

    Except for data value labels, the defaults are backwards compatible. That is, if you use SetGridColor() and do not use the new SetPieLabelColor(), your pie chart labels will display in the same color with all releases.

  • The legend background uses the overall image background color set with SetBackgroundColor by default. Starting with PHPlot-6.0.0, you can set the legend background color separately with SetLegendBgColor.

  • The legend color box borders use the color set with SetTextColor by default. Starting with PHPlot-6.0.0, you can use the colors set with SetDataBorderColors instead. See SetLegendColorboxBorders.

  • Legend text uses the general text color set with SetTextColor by default. Starting with PHPlot-6.0.0, you can set the legend text color separately with SetLegendTextColor.

SourceForge.net Logo

This version of the manual was produced for the PHPlot Sourceforge project web service site, which requires the logo on each page.

To download a logo-free copy of the manual, see the PHPlot project downloads area.