I made the suggestion that it should be displayed somewhere on the battle tab in guild wars itself. This is where it would the most relevant because the day’s color does not necessarily coincide with the color of the battles you are doing at the moment. Guild mate of mine already skipped a day and did the current days colors battles while he still had yesterdays queued up. Oops.
The display for which color day it is needs to be on the 5 battle screen associated with the guild being faced. It can’t be anywhere else because people who don’t do their 5 battles every day will have the wrong color shown.