All colors are specified in terms of a 24-bit color value, represented by the class TRgb. This 24 bit value is mapped down to device-level values by the graphics device or printer driver.
Note that:
Colors can be specified logically (for example the window background color), as well as physically. The UI Graphics Utilities API contains a list of logical Colors (TLogicalColor) and provides the means to convert them into RGB values.
The window server defines display modes that represent color resolutions. In each display mode, as enumerated by TDisplayMode, a unique index can represent each physical color supported. TRgb can map such indices onto a full RGB value.