Kim,
You aren't late - its the first block! I didn't start until late last week and finished my block on Saturday. Use any colors you want - there certainly is precedence for using dark backgrounds in Baltimore album (BA) style quilts. Many BA quilts were made with only red and green fabrics so most of us are rather "out of the ordinary" when we use lots of colors - and there certainly weren't any batiks in early BA quilts. Part of the fun I see in doing this BOM is that we all start with the same pattern and then make it our own - the differences are all amazing and beautiful.