For a clay tile roof I would prefer to have cement in a more similar color to the tiles than gray. The tile manufacturer recommends painting the cement but to me that is not appropriate on longevity grounds and the fact I plan to do water catchment. I was reading getting red sand is a very good way to go. Is this available in Thailand? If not, how about cement dyes?

Don't know about red sand but there are lots of cement coloring powders around.

And there is lots of different colored red clays that can be added to the cement mix up north and probably elsewhere in LOS.