I use lots of different brands, but sort them all into 3 colour ranges: reds, yellows and browns; blues & purples; turquoises & greens.
Two reasons: firstly, I'd never find the colour I wanted otherwise and, second, because the coloured dust causes cross-contamination and you soon get in a right grubby old mess.
So, last week, while I was ill and so had a pocket of time, I emptied the whole tray, and cleaned out the ochre crumble with a wet cloth (yellow mud everywhere - lovely). Then I wiped every single pastel stump individually, even the teeny bits, half the size of your little fingernail, which are great for doing really fiddly bits.
Colours came to life again and I unearthed several purples and blues in there, also masquerading as yellow!