Did you harvest by top cropping or from the bottom of the bucket?
When I top crop, I usually get a predominantly single color layer of yeast at the bottom of the jar of boiled, cooled washing/storage water. However, I have learned to follow the standard advice and wait long enough before top cropping, like 3rd day of fermentation, especially if a big beer, so I don't remove too much yeast, especially if getting blowoff on a big beer. If you top crop you want to ensure you don't remove so much yeast that the beer has a hard time to completely attenuate. But it is the best way to get just yeast.
There are trade-offs as to how you collect yeast. I know that a lot of guys who collect slurry rom the bottom of the bucket after racking off the beer, top it off with the washing water, refrigerate it, and don't worry much about the amount of trub along with it when they rack new wort on top of it, without much of a problem. I would assume that this method does pose a higher risk of autolysis if leaving the second beer a long time in primary.
I don't top crop if I use anti-foam drops, since there's not much of a top layer of yeast.