/cgl/ - Cosplay & EGL

Hey gulls, need some help.
My hair is currently dyed colour on the left, and my natural hair is colour on the right.
I love love love this hair colour and it makes me look so much better than my natural brown. However, I've recently developed an allergy to chemical dyes so my scalp is terribly itchy and my hair is full of dandruff.

Is there any way I can keep up the colour without using chemical dyes (for example with henna and cassia)? Or am I doomed to forever 'glossing' my boring, ugly hair? I don't want an unnatural copper red or a mahogany, I just want to keep the colour I have now.