Managed to finish this Reaper Bones Kraken. I tried for a tinted blue base to give the feeling of underwater, but kept the kraken itself in strong contrasting colours.
Here are a number of work in progress photos (and the full size versions of the above photos at the bottom):
The base was actually painted in normal colours, and then tinted with blue paint via an airbrush.
I mixed the original colour with blue to dry-brush back up the texture, and also used washes to tone down the blues.
Kelp was added using foil and dressmaker pins, and then airbrushed and added to the base.