That gluon emission and absorption change the color charge of a quark is a foundational definition within quantum chromodynamics and requires no citation.
The claim describes a fundamental rule of quantum chromodynamics (QCD) where color-charged quarks emit or absorb colored gluons, thereby changing their color state to preserve overall color neutrality. This is a definitional and basic physical fact of the Standard Model. Following the instructions for STEP 0, trivially true statements by definition or direct disciplinary consensus are classified as COMMON_KNOWLEDGE, requiring no papers and leaving indices empty.