I have quite a few scars, of different shapes and sizes, in various places - not the scalp though.
Well, not yet, but yesterday I just got a job offer for this summer, and I hope it can help me pay for something this winter

First, about the gel, mmmmm just wanted to help. Many people don't know about these gels, or think they're just cosmetics. I also used Cicaplast and I noticed results.
You say your scars look red. How so? How big and deep are they? Have you ever had other big scars before? Does it long much different? Some people do get cheloids - mostly African Americans, but also some Whites with unlucky genes. I once got a cheloid. Google for cheloids, and make sure it doesn't look like one.
If it is like this example on a white skin, stop reading and go talk to a doctors:

Now about the scar itself, something totally unrelated that you may find interesting. Silicone dressing are popular because most people have small scars. Very little is known about how they work. It could be due to the small pressure the dressing applies on the wound. A less known trick is that all scars are sensitive to pressure (
http://www.ncbi.nlm.nih.gov/pubmed/10550323) not just the burn scars, but surgical scars too. I have first hand experience with that, but a picture is worth a thousand words, so I spend a good hour and a half on google (because I don't want to post pics of my scars, sorry I'm very shy about that).
Look at the following image:

I tried to find better examples but I couldn't find anything better. In the middle of the scar, it's barely visible, because that's where the belt did its magic. I can tell from experience it does work. Where my underwear elastic stands, my hip scars are small, where the belt goes, my scars are almost invisible.
It worked for me, but it may or may not work for you. I don't know how well it would work with scalp scars, but I'm seriously considering FFS and based on my experience with my other scars, after it has sufficiently healed, I do consider wearing every night a non plastic swim cap with something inside to apply further pressure. That's
my plan. Once again, may or may not work for you.
About the dye, the bleach is aggressive, yes. It tingles well enough, even without any scars, that I sure would not take that risk. But grease does stops the bleach. I know because I do a complex coloring pattern and I want to protect some areas from the bleach. No reason why it would protect hairs but not the skin too.
If you want to be extra careful, go to a professional colorist, and ask to avoid putting bleach on the scalp. I often ask to avoid the scalp because I want to keep my hair healthy for a long long time.