This is really cool -- I think you have the look 'down pat'. Ultima 4 was my first PC RPG, and remains a favourite, and number 5 was a very impressive sequel, so I love what you've done so far.
I recently found a site that's dedicated to the crafting of 'vintage' RPGs, like Ultima -- here's a link to it's
fourth article. It's pretty text-heavy, but it has some cool pictures of the Ultima 'line-of-sight-shadows' system in action, near the bottom. I don't know if you're still planning on making this into a working game, but if you are, I hope you don't mind touching on the programming aspect a bit, as well as the graphics!
I love your palette, too.