The dark red are frequently single barred. This is a source of contention for me as true breeding rhodebar roos should be double barred (thus making them appear lighter). One of the reasons you see both is that in some countries it is common to "show" the single barred males because some people consider them more striking. Apparently those who show single barred males use their double barred males for purebred breeding pens.
Some will argue that a rhodebar cock can be single barred or double barred. I disagree. .. the single barred will not breed true 100% of the time.
So. .. there are many ways to skin this cat. .. Just depends if you want the skin or the meat. ;-)
with selective breeding one could darken the tone of the males, and outsourcing the Dark Barring gene from other sources would also do that, but will set you back a few time..