Reloader-10

These guys can mill the slide for you; https://suarezinternational.com/suarez-red-dot-sight-package-sig-p220-226-227-229/ And EGW has a mount that will replace the rear sight to allow a red dot to be mounted; http://www.egwguns.com/pistol-scope-mounts/viper/venom-sig-220-10mm-hunter-sight-mount-fits-burris-fastfire-and-docter/

I installed one of their bearings on my 550 and it is a bit smoother. I can tighten the shell plate down to remove any lateral play, and still have the shell plate spinning freely, whereas I couldn't get all the lateral play out previously and still have the shell plate turning freely.

Red v. Green fibers may really boil down to the individual user, and their specific eyes. Typically Red will be picked up faster for most people, and at longer distances due to the longer wave length of the light (hence why stop lights and signs are red.) In this case it seems the idea of a fiber optic rod in the front sight is to create maximum contrast against the black sight, in addition to providing the brightest point in your field of view (your eyes will naturally track to the brightest object). Here is an article on the science of the eye that explains it better than I can. https://visual.ly/blog/the-use-of-yellow-in-data-design/