Sweet talk your way into the chemistry department and ask if you can photo a demonstration of pH indicators. Take care around some of the solutions. To get some clour transitions you need to be very acidic or basic.


Or more 'plain jane' photo chemistry related:

Violet - potassium permanganate bleaching baths - mix from sctatch - not usually a commercial product.

Blue - Iron toner - again mix from scratch.

Green - copper toner - another mix from scratch

Blue green and violet are also the colour you get off of different RA-4 papers if you run a roller processor with a prewet first tank before the developer.
Manufactures provide an overcoat dye to fine tune the emusion reaction curve and speed of different layers with ra-4 paper.