Male House Finches get their red color from dietary carotenoid pigments.
Variation in male HOFI color (red, orange, yellow, none) can result from
different carotenoid sources, differences in amount of carotenoids consumed,
parasite load, etc.

Googling the terms "house finch carotenoid red yellow" will net several
papers (in pdf form) on the topic.

David Wright
Miami Shores

PS:  Carrots get their orange color from carotene; it is claimed that
"overdosing" on carrots can turn a person's skin an interesting
yellow-orange color.

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