Today I blocked in the major color shapes. I actually got a little carried away, putting in more detail than I should have at this point. By comparing to the postcard, I can see that the building is way too bright. If I had just stuck to bigger shapes, this would have been just as obvious, but would have saved me some time, since I now have to go back and go over everything here.
I think subconsciously I wanted to see what it would look like brighter, but in doing so, I think I lost out on the impact of the original sketch. The learning process continues.