Being common names, not scientific names, red head or orange head are essentially interchangeable in common usage these days. There's some documentation out there of an early mistaken collection location in addition to Tapajos (Araguaia, a different river) and some attempted to distinguish one location as red head and the other as orange head. There is also some documentation of another population in a Tapajos tributary and, again, I've seen attempts to say one is orange head and one is read head. I've also seen some say that 'orange head' is the original and correct name and 'red head' is incorrect. Then again, others are calling the same fish "orange cap".
But until this fish is officially described and logged in taxonomic lists, imo red head vs. orange head debates are essentially hobbyists or others of varying expertise splitting hairs over two popular, common names, neither of which is official or scientific yet. In any case, in common usage the names are being used interchangeably and most in the hobby are calling the same fish red head or orange head according to their particular personal preference or whim.
As far as the red/orange color, ime it gets better with age until the fish is 2-3 years old, so if you have young fish, be patient. And, as mentioned above, color also varies a bit with mood, preparing to spawn, etc. I also find really clean water makes a difference-- these fish like a good water change ime-- and there's always the food debates over which foods give you better color.