"...ok maybe not possible, but will the food coloring hurt the gecko?"
When someone told you no the 1st time...this statement implies that you would do it anyway as long as it doesn't hurt the gecko (supposively)...
and yes it is animal abuse...
an exmp.
ever watch the beast master movies? the 1st one or two featured a black tiger...a DYED black tiger...the last few (I don't recall how many there were) they had a NORMAL tiger because their black tigers were dieing from the dyeing...and they got into some big trouble for it...
another exmp.
back when my mum was a kid (some of you in your 30's - 40's might remember this) they used to dye baby chicks and sell them at Easter. guess what? the chicks would die from the dyeing within a few weeks, and they stopped doing this too...because it's abuse...and they got into trouble over it...
I have no clue how old you are, I have no clue how experienced you are. but you must understand how wrong that is. I really believe anyone with common sense would realise that confinscation of the animal(s) and fines would be the only thing resulting from the idea.
*shrugs* do what you must I guess. learn from trial and error I guess. just know the consequences if you get caught. and learn from what others are saying, you will not be producing any new morphs or color phases by trying to cheat.