I think I will do it in 'Gloss Black!' Should go nice with the silver OTA and all the Chrome & Brass fittings I am putting on the Mount. And as Jeanette said, a dark colour will reflect less stray light. Also Black items cool quicker. Not that it should matter with a mount, but you never know!!
I won't use 'Matt' black as it's gets dirty & dusty easily and Gloss is easy to wipe clean. And Gloss is SHINY!
If I don't change my mind in the next week before I get to the paint shop, It seems that 'Gloss Black' is the go!