Can we directly stimulate M cones in retina with current technology?
You've probably seen the news reports by now, in which researchers targeted and stimulated individual cone cells in the eyes of volunteers: "The elementary representation of spatial and color vision in the human retina" Ramkumar Sabesan, et. al. (2016). This experiment is the first time that researchers have targeted and stimulated individual cone cells. The experiments mostly involved L- and M-Cones, though the published research noted the response obtained from S-Cones, too. The researchers used 543 nm laser light (25 nm bandwidth) and an optical tracking system similar to what astronomers use to correct atmospheric distortions. So, yes, the technology exists, but it looks like it is so new in this application that no one has performed other experiments with it, yet.