I was on that quest for a 4" Plinker as well, looked for months and couldn't find one. Then lo and behold one showed up at the local range as a rental. And they wouldn't sell it to me. But I eventually found a 4" LNIB Taurus 94 that I like very much.
My wife had a 2" Plinker. She has trouble seeing the sights on a Ruger LCR. She thought the red fiber optic would have helped but it did not. I even asked a gunsmith about doing what you suggest, finding a green light pipe for the Plinker. He said it was possible but he needed to see the gun. However I lost patience and sold it off and of course now I regret it. Maybe thats why I was so determined to find another Plinker.
Maybe invest in some Hi-Viz or other manufacturer and experiment with it.
BTW: I called Rossi CS and asked who the supplier of the light pipes were, they told me but have forgotten. The company did not reply to an email. dropped it there, never tried to call them.