You can use a DTM to find a unique location, such as in D/DTM walking, but instead of using it to walk, you can use it to get the road colour or you could just use a D/DTM walker. I'm sure I saw a tut for it in the Intermediate/ Advanced section, but I'm not 100% sure (check the tut list, would be there if anywhere). If you do just use the DTM to get the road colour, you can then store that as a global var (as in declared at the beginning of the script) then use that instead of an actual number in all your walking procedures (which would save some time in the scripting, but does make it likely to faill 100% if someone was standing on the spot it chose to get the colour from - if that makes any sense).
By reading this signature you agree that mixster is superior to you in each and every way except the bad ways but including the really bad ways.