Not quite at hand, to be honest, but I seem to remember it was somewhere in Cajus Bekker's book Angriffshöhe 4000, but I might be mistaken. I'll try and find it again sometime soon.
You are definitely right that the MG FF 2cm cannons used red and yellow tracers, the blue colour was widespread for the 'later' MG-151 cannons, though.
It could be that it was meant like that back a long time ago in FC1, but it doesn't really hold true. A Cobra APC fires green tracers, for example, from its only weapon.