It's been a long time goal of mine to have a rainbow mohawk, and because I already had a mohawk when the supreme court ruled on gay marriage, I figured it was about time to achieve some goals.
This is by no means a definitive guide, but rather what worked for me. I didn't find a ton of info on creating a rainbow mohawk, so hopefully this will be helpful to someone else.
Trustworthy friend (optional, but recommended)
Hydrogen peroxide (depends on your hair, I had 3% on hand)
Conditioner (optional, probably should be white; mine was light blue)
Hair dye (I used Ion Color Brilliance, red, yellow, and blue)
Disposable cups + toothpicks
Hand mirror (optional if you have a trustworthy friend (Mine is a purple, heart shaped mirror from a game called "pretty pretty princess".))
Hair gel (got2b glued works well)
Step 1: Cut the 'hawk
I didn't really take pictures of this step because I did it on a whim, but here's a picture of what my hair looked like before, for color comparison, mostly. If you've never cut a mohawk, it's a good idea to ask a trustworthy friend to help, but (as with the dying) it can be done alone if you go slowly and use a couple of mirrors.
Step 2: Bleach
I used peroxide (3%) mixed with baking soda, and eventually I found that adding a little conditioner to that held everything together better. I left that mixture on my hair for ~1 hour and then washed it out. Going out in the sun for a while with it in seemed to help a little too. I did that 4-5 times over a few days, and it certainly lightened, probably to around the light red hair I had when I was a little kid. If you have dark hair, you might want to invest in better bleach, and if you have lighter hair you might not need bleach.
(Of course, make sure you wash well, and don't get the bleach on your skin too much. My peroxide was a very low percentage, but it was still a little irritating after a while.)
Step 3: Section Hair
I definitely fit the stereotype of dudes not grasping the subtleties of color, so I opted to use the six colors that are easy to think about. Because I cut my mohawk myself, and on a whim, it's wider in the middle, and I had to use 2 hair elastics for the green section.
Now is probably also a good time to put a little vaseline or conditioner around the perimeter of the hair, so that your forehead and other bald areas don't get dyed.
Step 4: Mix the Dye
I bought three tubes of Ion Color Brilliance Brights hair dye from a beauty supply store, thinking I could just mix the primary colors to get any color I needed. It mostly worked, although the red is much stronger than the yellow, and I had more trouble than I should have getting a good orange, especially considering what color I started with... :/
Everything else mixed easily with a toothpick, and I ended up using about as much dye as is in the green and purple cups in this step's picture for each section of hair.
I had read online that this brand of dye smelled "good" which apparently means that it smells like off-brand dish soap, which is certainly better than what I was expecting from a hair dye.
Step 5: No Mr. Bond, I Expect You to Dye.
Again, this step could be made more efficient by the addition of a friendly helper, but if you are like me and don't trust others with your head, it can be done alone. Wear gloves to apply the dye; it's definitely thick enough that you can put it on without brushes, and the sections of hair will stand up in little spikes, out of the way of other sections. (Not that I would suggest not using brushes if you have them, I just don't have any.) It took me about 40 minutes to do my whole head, but this is the first time I've dyed my hair, and I would never claim to be a speed demon.
Because my hair was still a little orange, the blue went on a bit greenish (which is why I spent so much time on that section) and it'll probably fade out a little green.
I've attached a high speed video of the application process.
Step 6: Rinse the Hair. Style the Hair. Wear the Hair.
I had the time, so I left the dye in for about 3 hours from when I finished applying it. In that time I mowed my lawn, and the dye was so thick that it didn't run with sweat, and my hair stayed exactly where I had put it.
When I finally rinsed the hair, I ran it under cold water and rubbed the dye out until the water ran clear-ish, dried it a little with an old rag, and wiped off the vaseline that was left.
Mohawk pro tip: put your shirt on before putting up your hair...
I've had good luck with got2b glued hair gel, especially the one in the black tube.
I would definitely recommend putting something over your pillow at night. (I used the shirt that I wore while applying the dye.) I haven't had anything rub off, but I'd prefer to take extra precautions than potentially dye my pillow.
I'll update as the color fades.