THIS, my friends, is a Cresyl Violet stain!
Or as I like to call it...the 'Easter Egg Dyeing' of histology ;D
Just douse your freshly-sliced brain sections repeatedly in a series of chemicals - dye, ethanol, acetic acid, xylene - for VERY precise time durations each, and you'll get a lovely (and very colorful) visual of all the cells in your tissue and their morphology. (Unless you made a certain step too long or too short. Then your sections will look smeared or uneven...if they don't slide right off!)
Voila, fresh out of the oven!! (I REALLY don't recommend eating them though...)