Got to keep things reasonably simple for the school club - so I carefully chose d10s of just one colour, and d8s of another so that the boys couldn't get it wrong.
(Or so that I couldn't get it wrong with my duff eyesight). We already have d6 in the club cupboard (mostly white with black spots or red with white spots) so I just needed something distinctive.
D4 and d12 are fairly rare, so I didn't worry about them.
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As for colour coding units, well for 15mm (as my eyesight gets worse) I actually mark the back edge of figure bases with coloured paint and then colour code army lists to match. Just on the edge (easy enough with 2mm or 3mm mdf bases)