The sketch preview could use some other tweaks.
For instance, there's no way to see what a sketch would look like on different types of cloth or different types of walls (cellar walls are always white brick). This is important because background color can affect a sketch in big ways. For instance, look at this cape:

White pigment has been replaced by transparency to reduce crafting costs. This only works because the background is close to white.
It would also be nice to be able to preview painted wall tiles next to each other when you're trying to make a mural. This is less important though, it's only a mild annoyance.