Acetone this? (Update...Rarity how do I get this off you now?)

[Baby Sugarberry]

Paint can cause even worse problems down the road than what you're trying to cover up.  Definitely stick to sunfading.

http://mlparena.com/mlp/index.php/topic,330090.0/topicseen.html

[hathorcat]

I hope that the sun fading works for you! It also seems to be common for come G4s to have little plastic imperfections under the surface but I think this looks just like an ink or paint or colour stain. Cant wait to see the results.