[ooopdddddd]

Up and down quarks have names that make perfect sense, they are derived from the isospin which in turn derives from spin (spin-1/2 was the only other well-known object in physics that had the same symmetry properties). Which one is up and which one is down is the only arbitrary choice.

Using "positive" and "negative" would have been a disaster. What charge does a positive antiquark have?