Here is a rather blurred picture where you can see the border I added along the hypotenuse. I wanted something similar to the other egdes and I'm pleased with how it turned out.
A couple of days ago I stumbled upon a sale at my LYS, and returned home with a kilo of beautiful grey yarn. I'm making (and modifying) a design by Marianne Isager, Munken/Monk from her book Classic Knits. This is what my project looks like so far. I can't even remember when I last knitted intarsia, but it was probably some twenty years ago.