Its ok to have difference of opinion with practitioners - especially colonics people. You are not really paying for their opinion - just thier expertise/caring-manner.
I wouldn't say that yeast is yellow - mine has always been pure white.
There is a yeast/mucous interdependency since yeast lives in your mucous membrane, so whenever you get a lot of yeast out, you will also get some mucous out at the same time. But mucous is clear, so if it is white, then there is yeast present.
You should question what anyone tells you - be it me or Shelley, or your colonosict, or your doctor. Everyone is human and prone to mistakes.