This is all about to change. The Navy is changing from Summer/Winter uniforms to year round uniforms. The "Service" uniform wil be black pants with a Khaki shirt all year round. The "Work" uniform/jumper will be camouflage like you see the men and women wearing to Iraq. The Navy will have blue/grey/white in the digital camouflage.
The single service uniform should save costs on uniforms and packing/storage. The camouflage is to hide imperfections created while working (dirt/runs). Should last longer.
PS: My Dad (Armed Guard) ran the Navy Uniform Shop and Warehouse from 1963 until 1996. If you got a Navy Uniform or Accessory in those 33 years it went through his department.