Hey, that's a good idea! I never really thought about having the light change from top to bottom. I just got another idea, but I don't think I'll be able to pull it off in the short time frame I have for this.
I used Character Maker 1999 to make it. It's good for square/rectangle tiles, but not for Isometric, so it took me a while. If there were a program that could make an isometric selection, I'd use it, but I didn't have one.
I just did tiles like this, and kinda Checkerboarded them when placing them, like how you see in the right side of it.