It's really shooter's preference. I don't use a laser, but I did get a red/green dot sight that I leave on green at a low level for indoor. To me it's easier on the eye and it ends up being a more crisp dot. Red, to me, ends up being a little blurry
However, in a real world scenario with having a laser on a handgun your focus would be on the full target with the dot only going "noticed" where you want the shot to go, so maybe the full detail of the dot is not important
At the same time, there is some science to why green would generally be better. The human eye is able to differentiate more shades of green than any other color
Any specific applications in mind?