Skow, unfortunately none of the stores that stock paint near me had anything close to Mudstone. I've been glancing at my test pieces and the lighter colour is starting to grow on me a bit, though.
The black, brown and terracotta patches I did with just a water wash, I shall try again with less paint and Future (now that I have finally located some) and see how much difference it makes. 
I found that my final wash was REALLY dark though, and wasn't quite as..runny as I thought it would be. I'll try that again on the new test pieces with half as much paint, I think.
I might try and find a nice green/grey too and see how that works out. I'm aiming for dungeon with stone built out of rocks readily available (everything), not so much a grander style that sourced 
their stones. If that makes sense. 
Thanks for the advice though