The main reason there are less merles working sheep is that there are less merles full stop. You need a merle to breed a merle ie one parent has to be merle. There is no difference in their ability as working dogs to any other colour, good and bad. I'm running a merle at the Scottish National Sheepdog trial on Saturday
Thank you . Ran my LILAC tri (perhaps the only trialing lilac tri in the UK lol) today but ran out of time in the shed. Not due to her colour but instead my inexperience