Seeing as how the production of carotenoids to make those reds is a function of dealing with the stress of higher light, I would also posit, as illustrated in some extraordinary examples of ordinary green plants like Blyxa sp. turning blood red, that the myth of going lean on nitrogen, and in some other misguided cases phosphorous, most likely contributes to the stress which may help the red along.
My reasoning for this is that nitrogen is especially important for all chlorophylls (chlorophyll A being universal to all plants) because thats what really binds the massive hydrocarbon chain to magnesium. Reduce the ability to create more chlorophyll with lower nitrogen while at the same time the plant is bronzing to protect its organelles and tissues may be the key to really getting some of those reds that you swear must be photoshopped. In short putting stress upon stress to get them to redden. Not being a professional like Tom, I can only hypothesize. In fact, Tom if you're out there still, I'd like to hear you discourse on this statement, however brief it may end up being
. The root of the mechanism is light, though. That we can all agree on, I think.
My personal statement, is yes, absolutely correct that you can get reds with everything in balance but in generous proportions, light, CO2 and ferts. My other personal statement is be happy with healthy plants. If they color up, great! Just don't go chasing the dragon and setting yourself up for mass deficiencies and an algae explosion for a cheap wow factor or for the sake of keeping up with the Joneses.
"You are much better off with no numbers than meaningless ones. The minute you believe numbers uncritically, that is, without understanding how they're calculated and how well they measure whatever they're supposed to measure, you will generate a breed of employee who will produce numbers and not results. Your data-processing system will then serve not to describe reality but to lie about it."
-Micheal S. Montalbano