I recently noticed that a brooks professional saddle
on (cough) one of my machines in my garage
has gone bright green with some kind of low-profile
mould.

Bugger.

The saddle is rather soft and damp.
I've removed it and bought it indoors for some
TLC.

Has any seen this before?
Is it fatal?
Any treatments known?

BugBear (not wanting to buy a new saddle)