The label-icons on mail in the list-layout are 3px X 9px tiny rectangles of color that are very difficult to discern when the color-shades are similar, and I can differentiate between color well - people who are color-blind cannot and would not have any idea what tags are on any email.
Suggestion: add (or make as a configurable option) alternative easier-to-identify icons that are bigger horizontal color bars with the initial 4-5 chars of the tag-name over them. The icon and text-size should be dynamic based on how many tags you are displaying, 1-tag = fullsize icon/font, more tags = super-tiny text/bars.