rubican

from The Century Dictionary.

• Noting the color of a bay, sorrel, or black horse with light gray or white upon the flanks, but not predominant there.

from the GNU version of the Collaborative International Dictionary of English.

• adjective Colored a prevailing red, bay, or black, with flecks of white or gray especially on the flanks; -- said of horses.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• adjective of a horse Coloured mostly red, bay, or black, with flecks of white or grey especially on the flanks.