For color switching glitches, there was some point where invisible Reid switched to another character but the shards still stayed visible. Then going back to Reid manually he looked visible but I couldn't touch enemies until I became invisible then visible again. I think switching by performing actions would be what tended to make things weird happen.
Main thing I don't like about switching colors is the loss of a turn. I would almost always rather power through an enemy with a sub-optimal match up than lose a full attack. That doesn't mean that I want the mechanic removed! Just that the cost of switching should be lessened a little, not fully, because changing freely also feels unfair. Something like a weak follow up attack, or buff added when switching colors, depending on which one it is could have made it feel more worth it to me.
I did grab all the shards! I need to go back and get fewer this time around and see what terrible things happen!