I do think some young, healthy eyes could use the colors for a while but I bet by the end of even a day-long shooting class their eyes would be fried.  I wouldn't try to use them myself because my eyes are late middle-aged, still changing for the worse, and they would just confound my focus problems (which started actively and noticeably degenerating again around the first of this year.  My ability to see the front sight without my corrective lenses is fading.  I'd been in between using either close-up or distance correction for some time and that splendid time is ending.)

I still like the U-notch, and in fact intend to replace some square notch sights with those.  In principle I believe the human eye centers the front sight in the bottom circular part of the U much like it centers a front rifle sight in the full circle of a "peep sight," or full aperture rear sight placed close to the eye.  No ghosting involved here of course.  It makes me think that the old-timers who designed U-notches in what, the 19th century, were not as primitive as we might believe. 

In conclusion, these sights, with white rather than unnatural florescent colors, would be quite useful.