It looks like someone asked the same question last year in the forums and got some good answers, including example code:
http://exchange.ni.com/servlet/ProcessRequest?RHIVEID=101&RPAGEID=135&HOID=5065000000080000007D560000&UCATEGORY_0=_49_%24_6_&UCATEGORY_S=0
It's the first hit you get if you do a sidebar search for "surface color" in the forums on the NI site.
Hope it helps,
John Lum
National Instruments