hypo
- Hy"po- [Gr. ? under, beneath; akin to L. sub. See Sub-.] 1. A prefix signifying a less quantity, or a low state or degree, of that denoted by the word with which it is joined, or position under or beneath. Webster's Revised Unabridged Dictionary, © 1996, 1998 MICRA, Inc.
hypo- or hyp-
pref.
1. Below; beneath; under: hypochondriac.
2. Less than normal; deficient: hypofunction. The American Heritage® Stedman's Medical Dictionary
Copyright © 2002, 2001, 1995 by Houghton Mifflin Company. Published by Houghton Mifflin Company.
mel·a·nism
n.
Dark coloration of the skin, hair, fur, or feathers because of a high concentration of melanin. The American Heritage® Dictionary of the English Language, Fourth Edition
Copyright © 2000 by Houghton Mifflin Company.
Published by Houghton Mifflin Company. All rights reserved.
melanistic
Mel`a*nis"tic, a. Affected with melanism; of the nature of melanism. Webster's Revised Unabridged Dictionary, © 1996, 1998 MICRA, Inc.
Hence, the term "hypomelanistic" lends itself to relative interpretation, depending on your perception of "reduced", "deficient", or "beneath normal" quantities of melanin. My perception of hypomelanistic may be quite different from yours, but most can agree that when two animals in dispute are placed side by side, it's not difficult to detect "normal" from "hypomelanistic". I personally consider a "hypo" to be a mixture of complete or nearly complete absence of melanin, with the possible exception of a faint trace of melanin surrounding the tail blotches posterior to the cloaca AND because of this lack of melanin, a pronounced presentation of erythrism. Just one man's opinion! 
er·y·thrism
noun
a condition marked by exceptional prevalence of red pigmentation (as in skin or hair) —er·y·thris·tic /"er-&-'thris-tik/ also er·y·thris·mal /-'thriz-m&l/ adjective Merriam-Webster Medical Dictionary, © 2002 Merriam-Webster, Inc.
erythrism
E*ryth"rism, n. [Gr. 'eryqro`s red: cf. F. ['e]rythrisme.] (Zo["o]l.) A condition of excessive redness. Webster's Revised Unabridged Dictionary, © 1996, 1998 MICRA, Inc.
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