I don't know if I have a "favorite" Border Collie color. I like how striking the black & whites are, but I also love red & whites and tris... and I would LOVE a red or blue merle, someday. I suppose my fave is black & white, with lots of white - not predominantly white, just with long white stockings, lots of white around the chest, and a nice, distinct white blaze or even a split face. I also love black & whites with white patches or white creeping up on the body (like Eve). Gonzo has less white than I prefer, even though lots of people randomly call him "flashy"? But, mostly, my preferences are with type than they are color.
I love the coloring of this boy, with maybe a bit less white.
I LOVE bright, chromey blue merle Cardigan Welsh Corgis. Regis's coloring is perfect to me. I particularly like bi-blues, or blue merles with deep tan points. I definitely prefer tan points over brindle points. At first, I wasn't that into tris, but Fozzie made me adore tris as well, especially red heads!
Both of these pups are precious...
I think sable merle Smooth Collies are some of the most stunning dogs on the planet. With distinct, obvious merling. I love the blue merles just as much, though.
A beautiful sable merle boy named Oz from another forum I'm on.