Like social elephants, quarks only exist in groups with other quarks.
Individual quarks have fractional electric charges. However, these fractional charges are never directly observed because quarks never hang out alone; instead, quarks will form composite particles called hadrons. The sum of the quarks' electric charges in a hadron is always an integer number. While individual quarks carry color charge, hadrons are color-neutral.
There are two classes of hadrons:
Baryons are any hadron made of three quarks (qqq). For example, protons are 2 up quarks and 1 down quark (uud) and neutrons are 1 up and 2 down quarks (udd).