There are lots of threads about ombres with gel polish, in truth I don't think anyone has successfully mastered it. There are videos on YouTube etc with a variety of techniques but they all seem to be super time consuming and each nail takes too long which makes them unrealistic for busy salon environment.
I've not seen any successful pigment solutions either, they are always pigments with shimmers in, no good for those who don't want/like shimmers. I've tried a few matt pigments but I still can't master it good one, the white pigments are lumpy and don't blend well.
L&P seems to be the best solution for ombres