I usually avoid Detonator because it looks so short and tame, but on my last visit, I did it. It was insane, the intensity was overwhelming and knowing that it pulls 5.5G didn't help.
Due to this, I used to be scared to go on other drop towers, but when I did them, they were absolutely fine and I conquered my fear with ease.
Anyway, I'm just trying to make 2 points here:
1. Fears are usually triggered by a frightening experience that makes you nervous about repeating it.
2. Start with the tamist, and then work your way up. Don't start with detonator like I did (or Colossus in your case) because it will give you a false idea of what inversions are like. This could then frighten you further, to the point that you don't want to go any coasters with inversions.
This could be paralleled, to a boy in my class. He was petrified of going on a trampoline but we all told him that it would be fine, it's safe and he doesn't have to do anything he doesn't want to do. He got on, he was shaking and then he fell off, due to this bad event, he received false ideas about trampolines and never went on them again.