For plants that have the "Purple Gene" the easiest way to turn them is to ice their roots after you flush them... (I.E. about a week or 2 before harvest)...

The cold is what triggers most outside plants to turn purple.

Also, to learn Tissue Culture, I would start with edible mushrooms. It's a very easy way to get some of the science down, but maybe not the details. (My bet is that the solution for plants is different than the solution used to grow mushrooms (mycelium)