I've been thinking about dying my boots, but what would happen if you bleached your boot? Could you put something around parts so it could end up like a t-shirt or what?
Dip dying could def be done. you might be able to get a tie-dye effect using rubber bands around the shell.. OP bleach wont work, it will just damage the plastic, you can only make light plastics darker with dyes.
The most permanant method is dying you could colour them with spray paint but thats only as thick as the layer of paint which will get scuffed off and chip whereas dying the colour seeps into the plastic and wont be damaged by normal wear and tear on a boot.
Instead of rubber bands use hot glue and rubber cement. Dye the shells a lighter color first then squiggle the glue and then the darker dye. Then remove the glue/cement and it should look pretty sick.