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.
Hopefully this message will be attended by Nokia team.