Steve
I concur with my learned friend.
Even dry compound can fade the colour, brush a little bit more over a more heavily soiled patch and it will be like "vanish" but bigger. BUT THIS IS THE ONLY SAFE WAY TO CLEAN COIR.
Do not HWE, unless of course you want to own the carpet, albeit a lot smaller than it is now.
I have lightly LM cleaned these before but results are limited.
I could be tempted to try encapsulation with a CRB machine though.
SAFE and happy cleaning

Ken