Quarks and gluons are color-charged particles.
Just as electrically-charged particles interact by
exchanging photons in electromagnetic interactions, color-charged particles exchange gluons in
When two quarks are close to one another, they exchange gluons and
create a very strong
color force field that binds the quarks together. The force
field gets stronger as the quarks get further apart.
Quarks constantly change their color charges as they
exchange gluons with other quarks.
How does color charge work?
There are three color charges and three corresponding anticolor
(complementary color) charges. Each quark has one of the three color charges and each antiquark has one of
the three anticolor charges. Just as a mix of red, green, and blue light yields
white light, in a baryon a combination of "red," "green," and "blue" color charges is color neutral, and in an
antibaryon "antired," "antigreen," and "antiblue" is also color neutral. Mesons are color neutral because they carry
combinations such as "red" and "antired."
Because gluon-emission and -absorption always changes color, and -in addition - color is a conserved quantity - gluons
can be thought of as carrying a color and an anticolor charge. Since there are nine possible color-anticolor combinations we might
expect nine different gluon charges, but the mathematics works out such that there are only eight combinations.
Unfortunately, there is no intuitive explanation for this result.
"Color charge" has nothing to do with the
visible colors, it is just a convenient naming convention for a mathematical
system physicists developed to explain their observations about quarks in hadrons.