Kevin;

If you are using the old glass plate holders with the red sheet in the middle of the holder (it is usually wavy and not flat), this will serve as a good AH backing for slow blue or ortho plates. This is especially true if your subject is not back lit.

If you want to go "all the way", then the old guys back 100 years or so ago, got an oxonol dye, which is yellow orange. They coated the backs of the plates with the dye in gelatin and it washed off during processing. Often it was totally removed as they did not harden the gelatin.

Almost any orange dye can be used, such as a mix of Solantine Pink and Solantine Yellow. You can use food dyes which are really often Solantines.

PE