I've run plates through holders with red septums and black septums (the middle, backing part of a holder) and never found that the red does much to help. The problem is that the backing has to be in close enough contact with the back of the plate that there is no air space. In the early days the solution was usually lampblack or caramel coloring in gelatin or reusable applied sheets. The right dyes in gelatin came a little later and probably work the best, but whether or not more so enough to be worth it is certainly a matter of taste and not of necessity.

There are good illustrations of both irradiation and halation at toward the bottom of this page.
http://thelightfarm.com/cgi-bin/html...tent=04Dec2011