Wouldn't get too caught up in achieving the right colour, but definitely do as Stik suggested, take some image searches for ideas. With the recent turmoil in Libya, the news media has provided much photos of the region.
I think you will find though that results will show a variety of shades from the same location, is this indicative of different sands? Maybe, but I think more likely the result of different atmospheric conditions and time of day the photos were taken. There are different soil types out there (try a map search on soils of North Africa), but this is most prevalent in Tunisia.
Equally important, if not more so, is getting the texture right. Also, any ground weathering you have done on the vehicle should also be applied somewhat to the desert floor to tie things together. This way the vehicle looks to have driven through the area and not beamed into place. Most of all, have fun and post pictures!
regards,
Jack