Dan Harlan's a "Little RnB" has some good uses of a r/b double backer. After buying that I changed up a little bit how I use the R/B I usually carry in my decks.
I usually use it in an opener where I find their card by looking at the backs. Their selection appears to all of a sudden has a different colored back, then it changes back after they sign it. I used to ditch the double backer during the signing but now I don't mind leaving it in the deck for a prediction effect by Harlan later on.
I haven't used a same color double backer very much. I've mainly used it as a utility card switching in/out gaffed cards in a 3 card monte routine. I used it a few times with the tilt too in a ambitious card routine but abandoned that because of how I perform that routine. I have thought of using it to hide a card with a different back and have their selections back change similar to how I do with r/b double backer.