I've had this too! T-Gel do a gentler version of their shampoo - it's meant to be for dry hair. It's pale yellow instead of dark brown like the original. It smells better than the original, which smells a bit like tar : / I found it really calming on my scalp and it did help a bit with this 'issue' even though it's meant to be a dandruff shampoo.
Good luck, imported_Lady_Eagle! It is possible to get rid of it, or at least improve it.