Ravas,
I believe that DXF specification support by default a set number of colors in a 8 bit range, a set of them have special meaning (0 = by block, 256 by layer)
http://images.autodesk.com/adsk/files/autocad_2012_pdf_dxf-reference_enu.pdfNewer version's of DXF specifications allow for RGB colors, and we also support that.
So a predefined set of colors does help and I believe the CAD people do have specific colors for specific area's in drawing, but this can also change per company.. I can imagine that apart from colro naming (red, blue, yellow) I can also image people might use 'Wall, Sand, floor etc...'.
For us the issue of CMYK doesn't matter to much, if not at all since we are not operating in the prepress industrie and if it does happen, you can somewhat convert between both color models but this usually happens in the prepress software and doesn;t really concern CAD software.
Hope that answers your question...