What makes a
female change from vibrant blue-green colors to a
pale tan color with horizontal dark body stripe as
she observes a male in container next to her?
DESIRE!!! ;) hehehehehehehe...
If the male betta is a good looking young lad, the female will usually become shy, flustered, and possibly spill her drink, trip on her high heels, drop her handkerchief or find another way to get him to notice :). Come to think of it, a baseball bat works pretty good, too LOL.
Stripes are an interesting thing with bettas in general, but are especially noticeable with females. There are basically two types of stripes: Horizontal stripes and vertical stripes.