I know, I know, I said I wasn't going to do anything more with the Illusionist's Garb but my OCD kicked in so I had to arrange it with the standard (and prettiest) mage collar and also with the padded armor collar and pauldrons. Now this is a little rough because I cannot remove the shoulder pieces and strappings from the image so I just placed the new accessories approximately over the original to give an idea of how it would appear.
Left is my red and violet version with the standard mage collar in dark purple, and right is the seagreen and coral version with the padded armor collar and pauldrons. Both could look quite nice, I think the standard mage collar is more feminine than the padded armor pieces, but either could solve any open-back issues for male mages in robes, assuming of course that a male would wish to wear such colors in the first place. I'm thinking a male svirfneblin with blue or green hair might look very striking in such an ensemble.