So (English isn’t my first language so sorry for the spelling mistakes) The first time we saw dabi in the anime was near a Hair salon so he maybe dyed his hair for shoto/endeavor not recognized him and for the scars it’s Endeavor who abused him,With his blue flame he burned his own son kinda ha4 to explain but I hope you get the point
I get what you're saying but I think what's confusing is the fact that touya as a kid was losing hair color with the use of his quirk. Maybe like og said due to his quirk overuse causing biological issues or maybe activation of a minor version of the ice quirk.
Wait, those scars aren't from Endeavor. Didn't you see that Dabi's own flames burn him? In that scene when he's a kid and talking to Endeavor, He lit his hand with his fire quirk trying to do Endeavor's super move and his wrist got burned. And there is another time when he was over using his power as an adult and he got burned.
As for the original question, I don't think Dabi has an ice quirk because if he did he'd be able to regulate his body like Shoto does. Shoto doesn't get extra crispy because good sense and his ice quirk mitigates that.
to kinda put my word in here. It's a natural occurrence for hair to turn white under extream stress regardless of age. So stress here could basically be the effort he puts into meeting his father's standards and after shoto was born it probably got worse as he was discarded. Another thing is that he probably got his weak fire resistance from his mother so while his fire is strong his body can't handle it.
But why do I feel like he also inherited his mother's quirk since his hair transformed from red to white which also explains his scars, other than being burned by own fire quirk or the fire which caused his "death". He probably tried to lessen the burn my using his ice quirk but led to scarring himself? What do you guys think?