Color can be selected in several different ways. One of the is to create color maps with the makecpt and grd2cpt modules (see their own man pages). This is the method we use to colorize images, sets of points, etc. The other option sets the color via keyword/value pairs and is appropriate to color fill polygons, individual symbols, etc and the one documented here.
We may use this in modules that expect the color or fill keywords, then the value can be a string or a symbol with the color's name (or names separated by commas); a number in the [0 255] range to indicate a gray shade tone; or a 3-elements tuple (more tricky) or array (simpler) where each element contains the R,G,B component in either [0 255] or [0 1] range.
color=:red Single color
color=200 Single gray
color="#aabbcc" Single color
color="30/20/180" Single color
color="yellow,brown" Two colors
color=(30,180) Two gray levels
color=((30,20,180),) Single color
color=((10,50,99),(20,60,90)) Two colors
color=[0.118 0.078 0.706] Single color in [0 1]
color=[10 50 99; 20 60 90] Two colors
color=(:red,:green,:blue) Three colors
But there are other options that expect color in one of its elements. For example, to set a text font we may want to choose a color (i.e. not use the default which is black). Then we would do drop the color= and use the value in that other option value. For example font=(12, "Helvetica", (30,20,180)), where the color is the third element in the font keyword option.
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