PSL supports RGB, CMYK and HSL. Users can pick from a library of pre-defined and named colors or define his or her own using an interactive (HSL) display.
An interesting example of PSL’s attention to color detail is a command – “newDarkercolor, x” which defines a color x fraction darker than “color.” This is quite useful when dealing with transparency or shading a figure.
PSL supports, as you might note from the figures above, both axial and radial shading techniques.
Transparency can be dealt with in two methods. In one method the user selects one of a myriad of “codes” which are part of PDF to cause a wide variety of effects to occur. Note for example in the “Kennel” example that the dark crack on the background board shows through the “PSL” text written on the board. The second kind of transparency involves filtering out a range of colors. This is particularly useful, for example, in removing the colored background on a “mug shot.”
PSL also supports “Opacity” where a factor of, say, .05, would result in a 5% screen.
PSL users can set an intensity directive to reduce the intensity of all colors in an image (or line, or font) – the equivalent of screening to a lithographer.
And, of course, color is a data type meaning one has the ultimate control of colors based on variables in the data.
Color Control Samples