One of the problems with Mini "colours" (there are only two colours in any type or breed of horse, Black and Red [chestnut] everything else is a modifier or a dilute of those two basic colours, or a pattern.) is that different things express differently in different breeds.
Thus we have found that Smoky Black (Black with Cream) often but by no means always, shows up in Minis as a sort of dark coffee colour, and that Silver, unless it is inhibited by Cream, shows up with a much paler mane and tail in Minis, whilst in some BH breeds it hardly shows at all, and has to be tested for, thus making people believe it is "rarer".
The Miniature Horse has also become a real "melting pot" of patterns , modifiers and dilute, everything being crossed with everything else, until we do seem to have an absolute "rainbow" of horses!!!