There was room for feet and wing feathers, so I put them in. A simple purple rectangle would have been clearer. Here's where making your own symbols really pays. You still have plenty of scope for further invention. These miraculous little colour machines allow a rainbow of opportunities for colour coding.
Blackbirds can count up to five.
Human beings don't do much better than seven when it comes to remembering things. You can always add refinements when using five to seven symbols has become second nature. Quick bookmark for IE5 users. I've tried to make this information as accurate as possible. Please let me know if you think anything is not right.