Ive got the Serengeti Velocity ones with the brown photochromatic lenses and haven't found the adjustment of colour to be any problem (whilst completing my CPL training).
Also I have to say after using RayBan for a year previous to swapping to Serengeti (about 7 months ago) which I thought were great at the time, I have not looked back after swapping great pair of glasses and I find that the brown lenses are better as they don't block out as much light and the lenses also give a sharper image than the Ray Bans I previously used.