Regarding the DMC, when I was last there (1 year ago), it was only Harper Hospital (and Hutzel, I think) where the RN's had to wear navy. It was a change based on a survey that was done asking patients their opinions. Patients complained that they never knew who the nurses were (vs. techs, PT RT, houskeeping, etc.). The patients opted for first choice white. Harper opted for Navy and they switched to having to wear a large "RN" dangle from their badges.
At some of the other hospitals, various departments are required to wear certain colors.
For instance at Detroit Receiving ER, they also wore navy. RT's at DRH wore black. Ancillay staff (housekeeping) wore burgundy, as did the unit clerks lab coats. All surgical units (including burns) wore hospital issue seafoam green.