The phrase "hound color" refers to the coat color or pattern commonly found in hound dogs, which are usually breeds used for hunting. It typically describes a combination of colors, such as brown, black, or white, that can be found on their fur.
The breed's coat are seen in all allowable hound colors including black and tan, liver and tan, and red; darker colors being interspersed with lighter or badger - colored hair, and sometimes flecked with white. (soonervet.net)
The standard states «any recognizable hound color is acceptable», and blue is a recognized color in some other hound breeds, so it's not illegal — but it is VERY undesirable. (potomacbhc.org)