Solid colors, even whites, will always outsell roans or red/white marking or even black/white ones (not including baldie or blaze faced ones). I do understand that there are roans and paints that will perform well, but the problem here is that once a buyer gets burned on some that don't perform, they're really hard to get back. And most buyers that have been around long have been burned by buying a set of 300# clubby bred Shorthorn colored ones that never grow and/or cripple up when they do. So next time they find some big framey looking ones, then they couldn't get 'em finished. Sure there are black ones like that too, but if you say you'll never buy another black one you'd just as well get out of the business 'cause in this part of the world 80% + of the cattle that go through the sale barns are black.
If you can produce good performing Shorthorn colored cattle and can't get them sold right at the sale barn, then you need to find another way - go together with some other breeders if you don't have enough, but retain ownership on a pen all the way through. Keep the data (if it's good) and use it to help you and your fellow Shorthorn breeders market your cattle in the future. If that's not feasible, at least try to find a buyer who will come to your place and look at your calves (and their mama's and daddy's) and see that they have some future - they might give something more than you'd get at a salebarn.
One bit of advice, try to sell anything that's apt to get discounted when the market is hot - discounts will be alot smaller then than in a softer market. Also, the bigger they are the less discount for color alone seems to hold pretty true - if buyers can see performance still in 'em at 900#, that makes 'em a way safer bet for them than 500#'ers.
Edit to add - I was typing (very slowly) while Mark H's reply was posted, but I agree completely with what he said, too.