3. Match colors

This one should be obivous, as this is really just a rule for all of TF2. If your hat has a distinct color, make sure the FL is the same or complementary (ex. Purple/Yellow, Red/Green, Blue/Orange) color. That's the thing about the Fast Learner, since it's so basic, it's takes up half of the torso's color. If the hat is painted white though, then you can obviously leave it unpainted. So you better have a matching color, or it's just gonna look awkward and unpleasing to the eye.