Quarks come in three "colors" in the context of quantum chromodynamics (QCD), which is the theory that describes the strong nuclear force. The term "color" in this context is an analogy used to describe a property of quarks related to the strong interaction, but it is not related to the colors we perceive in everyday life.
In QCD, the strong force is mediated by particles called gluons. Quarks interact with gluons through a property called "color charge." Analogous to the way electric charge can be positive or negative, color charge can be red, green, or blue. These color charges are often represented by the terms "red," "green," and "blue" for convenience, although they do not correspond to the colors we see with our eyes.
According to the rules of QCD, quarks always combine to form colorless or "white" states. This means that in any observable particle or hadron, such as a proton or a meson, the combination of quarks must result in a color-neutral overall state. For example, a proton is composed of three quarks: two "up" quarks (one red and one green) and one "down" quark (blue). The combination of these three colors results in a color-neutral proton.
It's important to note that in addition to the three colors (red, green, and blue), there are also corresponding anticolors (antired, antigreen, and antiblue) that belong to antiquarks, which are the antiparticles of quarks. The combination of a quark and an antiquark can also result in a color-neutral state, such as in the formation of mesons.