You can change the foreground and background color of an object in a form by using the Set Color command. This command follows this syntax: SET COLOR ({*; }object; color{; altColor}). The color parameter (same as the altcolor parameter for listbox) allows you to specify the foreground and background color. It follows this formula:
Color:=–(Foreground+(256 * Background))
Below is an example code which shows how to change the foreground and background of a text variable to red and light blue respectively:

C_INTEGER(Foreground;Background)
Foreground:=Red
Background:=Light Blue
SET COLOR(*;"TextVar1";-(Foreground+(256*Background)))

Other predefined values for colors can be found at this location:
https://www.4d.com/docs/KTU/KTU00006.HTM