Decoration of "other" refs

Hello,

I have been trying to adjust the colours of log decoration, and I think
there's a gap in configurability.

guilt creates refs/patches/$branch/$file.name for each applied patch,
and there appears to be no way to colourise these.

Looking at the source, it appears that in ref_namespace[], the
configuration for the NOTES, PREFETCH and REWRITTEN namespaces also
don't specify a .decoration attribute, so will pick up a value of
DECORATION_NONE.

It's probably not feasible to have configuration for arbitrary refs, but
couldn't DECORATION_NONE turn into DECORATION_OTHER instead, and have an
option which could be customised to something other than white?

Thanks,

~Andrew