I wonder if novocolor II tints would jive with Tru oil? On its own (the tint) will never dry, but mixed with a stain/paint it will. I like the linseed oil idea; I'm gonna try mixing a few small batches up with various colorants and see what the heck happens. Might even be cheaper than getting custom stains mixed up.
Have also wondered about mixing colorants with polyurethane, lacquer, spar varnish, etc. to create your own tinted clears. I bet a water base clear would look nice, but the main concern would be if it's sandable or not.