I would love to see each block framed in a small border maybe 1/2" wide or less and then blue sashing. The problem I have with the blue sashing is the river and lake seem to disappear into it. But I think a small frame would solve help your cute blocks to stand out more. Now for the issue of what color to chose for the "frame". The red would certainly pop and keep in with the theme of bright primary colors. But it may be too much pop. I have to audition things like that.