I looked through a new Nokia document named "Developer Platform 1.0. for Series 40 and 60: Known and unknown issues" and was surprised to find that a bug reported quite a while ago is not mentioned there.
The summary of the problem:
setColor is ignored for offscreen graphics (obtained with getGraphics from an Image) : text and lines are drawn in default black colour (observed with Nokia 3650).
The original message also contained the sample code. The URL address of the thread is give below.