The reason for the colored chakras in the Western illustrations of kundalini has to do mostly with extrasensory experience during the use of hallucinogenic drugs. Many of those diagrams were done on the basis of subtle experiences while using the substances.

Yogi Bhajan taught a valid kapalabhati/bhastrika pranayama method but he did use Sikh mantras. However, those mantras were in Punjabi which is a sub-language of Sanskrit and Hindi.

Yogi was a Sikh but in my experience with him, he did not require that one become a Sikh if one only wanted to learn the pranayama.

Later his teachings of pranayama went through alteration, especially after his demise.

I agree with B Adjodhya's statement.