Pembroke Welsh Corgis come in 5 basic colors, usually with white trim: Red, Red-headed tricolor, Black-headed tricolor, Sable, and Fawn.
Genetically, Red is dominant to Red-headed tricolor, which is dominant to Black-headed tricolor. The genetics of Sables aren’t fully understood. Some opinon that Sables have a “weak” Red gene that allows a tricolor gene to be partially expressed. Fawn is a very light Red.
Red: no obvious black hairs
Sable: Red with dark hair showing on withers, sometimes black “skullcap” on head, base of tail, along shoulderblade lines.