But if the seller didn't even know the proper names of the colors they were selling how could they know the true value?
The Shetland Sheep Society, now run from the "mainland", and the Flock Book in Shetland itself are somewhat divergent. In Shetland, very few use names other than those used at Flock Book shows and sales in Shetland - ie, White, Moorit and Coloured (other). (Except maybe farms whose business was selling fleece and yarn, eg Foula, Vaila and Uradale.)
I have been to Shetland Wool Week three times - 2014, 2015 and 2019, and on each occasion have spent as much time as possible with Shetland sheep and those who farm them, breed them and use their fleeces.
I always spend some time with Oliver Henry (retired MD of Jamieson & Smith Woolbrokers, and until the last 4 years, their chief grader and sorter of Shetland fleece. Woolbrokers buy the clips from farms registered with the Flock Book, and Ollie often a judges at Flock Book events.) It was only on this last trip that Ollie has started to use some of the colour names on the Shetland Sheep Society tea towels, probably because J&S under the management of Adam Curtis is being run as a more "marketing aware" operation
Anyway, to a lot of people who have been in Shetland sheep for many decades, generations even, these new-fangled colour names are all a bit of nonsense

So a longstanding breeder may well not use much outside of black, grey, white, moorit and katmogtet, gulmoget or maybe flecket for markings.
Which is not to diss those who do, at all, but to explain why some sellers might not use the other colour names.