tl;dr - ITS POSSIBLE BUT HARD!!
Alright, so fun little tutorial on how to do a good job dying wigs with food coloring.
I know alot of people like myself who either, can't afford a new wig, or professional dyes.
My mother does lots of baking, so she has tons of bottles of food coloring, and the such. My journey started in the kitchen.
First, I needed to turn my light, light pink wig into an orange wig. So first, I grabbed a color wheel and did some research, I needed to use one drop pink, and 7 drops yellow for mine, now you dont have to be SUPER exact, I just had 2 chances at it, you might have more.
I tried with water, and here's the main reason you dont use water, or dye it like normal hair.
1. Water will drip because its to liquid-y and it will not get the roots, so say you dye a white wig red, it'll all drip out so the roots are white, and only the tips are red. Its good for gradient's though.
2. Conditioner just washes out, its not like normal hair.
So, what do we do?!
well, we need something we dont have to wash out, and something thats thick enough not to drip out of the roots.
So I went to the laundry room, and for my second try, I used laundry detergent. My laundry detergent was blue, so I grabbed fabric softener. I added the colors to that.
Be warned though, there sometimes can be clumps of food coloring, so just be warned of that! :P
Next, I submerged the wig and left it for about 10 minutes, I then took it out, layed it on my styrofoam head, and let it dry for about 3 hours.
I then brushed it out, and i sprayed a tiny bit of water, (tiny bit!!!) just to make it easier to brush through, as it was tangled.
I don't have any pictures, but I can tell you that the roots were the proper color, and everything! just remember that the color can, and might all come out in one wash.
another small tip is that if the roots don't stay the same color, or something like that happens, then wet a paint brush, and lightly run it over your food coloring, then paint it onto the wig.
Laundry detergent and fabric softener are the most easy, and successful ways I have found at dying wigs on a low low budget :)
Bye for now! If you have any questions, you can put them in the comments, and I might be able to answer. Byebye for now!
So I'm gonna give some critique to this method. I hope I don't come across as being too harsh, but here goes.
1. Cosplayers don't use professional dyes to dye wigs*. They mostly use things like sharpie markers and alcohol or fabric dye. Yes there are people who use more expensive inks, but in general you can dye a wig with a bottle of rubbing alcohol from a dollar store and a couple markers.
( * To my knowledge, there are some sites that sell wig dyes so I guess you could call those "professional"? Most people just DIY it though )
2. You didn't specify the type of food coloring. Like do you mean the liquid kind in the dropper bottles or the gel type used to color things like frosting?
3. In my experience, food coloring stains like no one's business. As you stated, the color will most likely come out in one wash. So it would seem that there's a big risk of your wig staining your costume. Even without being wet, just rubbing could transfer dyes.
To be fair though.. methods like sharpie dyeing can also stain costumes. But those methods have a step of rinsing the wig until the water runs clear in order to prevent this from happening.
Critique aside though, I do think it's super awesome to experiment with new ways of doing things. It could very well be that this method does work perfectly, however I do think that you should test things like how long the dye stays, if it transfers easily etc and share those results.