The default colors for priorities as seen at http://localhost:8080/secure/admin/ViewPriorities.jspa are very poor choices for colorblind people (10% of men). I realize these can be changed, but why not pick some defaults that work better? For example, how about these:
3 #009900 (no change)
4 #006600 (no change)
Also, please get someone to check the colors locally - I bet you a beer you have a colorblind guy on staff somewhere!