What color should harvested yeast be?

[pmkealiher]

I've harvested yeast a few times before and thought I was doing it right. This time I washed it a few times and got rid of the obvious sludge that was with it and thought I had good clean yeast. But now there is two layers again, one being kind of brown and grey, and another thin almost pure white layer on the top which I'm assuming is good yeast. Is the brownish layer (which is most of the jar) not good yeast?

 

[LLBeanJ]

The nice creamy white layer is indeed the yeast. The darker grey/brown layer is trub, not yeast.