Numerical codes are used since most AKC paperwork is now being done online.
The acceptable breed colors and markings are already set up in the AKC database.
If you go to this link www.akc.org/registration/colormarkings.cfm and pull up Rat Terrier, you'll see them listed. (AKC allows a maximum of 18 colors and 9 markings.)
Here are the listed 18 colors and 9 markings, along with a brief description of each marking.
COLORS (18 colors)
Black & White 019
Black White & Tan 034
Black Tan & White 030
Blue White & Tan 066
Red White & Sable 158
White & Apricot 200
White & Black 202
White Black & Tan 219
White & Blue Fawn 334
White & Blue 288
White & Chocolate 287
White Chocolate & Tan 397
White & Fawn 207 (aka Isabella/Pearl) Note: Black masked fawns are faulted.
White & Lemon 211
White & Red 214
White & Silver 216
White & Tan 197
MARKINGS (9 markings)
Badger Markings 001 (Calico: tan face/broad creeping tan markings and/or darker back and top-skull. MUST have tan.)
Blanket-Back 084 (Saddle-type piebald marking over back & ribs, with white over loin & shoulder and on legs, brisket and stomach. With or without Tan markings.)
Irish Marked 115 (Tuxedo: predominately solid from shoulder to tail; White chest/feet/with White full or partial collar marking with or without Tan markings.)
Piebald 025 (White with any shape, acceptable color, or pattern -- with or without tan markings.)
Sable, White Markings 067 (Any white markings, in combination with dark tipped, overlay of sable hairs on base color.)
Solid 110 (Predominately solid - self-colored with minimal required patch of white (1-10%) on body, OR complete "Excessive White" piebald with mottled skin/ticking & dark nose. With or without Tan markings or tan flecks.
Spotted Or Patched 106 (Any color with piebald pattern mostly white: dark head/mask, or eye patch/s with ovate/rounded markings and/or jagged/patched piebald patterns. With or without Tan markings.)
White Mask, White markings 104 (Near solid "Excessively White Piebald" but has only small patch/s of color. A few spot piebald)
White Markings, Tan Points 030 (white markings with any visible tan trim. Use with any bicolor listed above in COLOR, to denote individual as tricolor.)