Bernd Uhlenberg This Kit is not a GTS, it´s a GTB. Revell named it wrong at the time.
You have to paint the targatop black or you can cut it out.
26 April, 16:55
Daniel H I converted the instructions images at Bob's link into a PDF for easier use. The scans aren't the best, so some text is only minimally legible, but the step-by-step is clear enough to follow.