The Epson nozzle check pattern is not always the best way to tell whether color is being applied evenly. It is useful to print one of the "purge patterns" available (or make your own with vertical bars of 50% gray, black, pure cyan, magenta, yellow, red, green and blue) using "Plain Paper" and "Normal" settings (with ICC turned off in Qimage and Epson driver). I turn on "Gloss" (to "Full" rather than "Auto") just to make sure there is no contamination or color contribution from the gloss optimizer. You should get solid bands of uniform color; if a nozzle is misbehaving it's readily apparant by the narrow "lines" that appear in some of the colors.
The "Blue" ink is actually a shade of purple (to my eye at least) so don't worry about that one.
I used to have a little file like that, back in the continous feed days.. a couple computers ago. Is there a file you could send me, I don't know how to setup the pure colors to print.