I had a pair of orange tread D'Allesandro Criterium tires in the mid 70's. Clement Criterium Seta Extras also could be had with orange tread. Wolber made some tubulars with red tread around the same time. I seem to remember that a justification for this was that a non-black tread would not build up heat and hence pressure as much as a black tread; don't know about that, but they sure looked neat with my green Gitane!
Best regards,
Wes Gadd
Unionville,CT