The color doesn't dictate the charge status on the default themes, it is typically how "full" the icon is, IE from left to right, is it full of color or empty? If it is full and yellow, then the battery is full, whereas if it is just a frame or box that is empty, then the battery is low.
It sounds like your meter is fine, you just may not have payed much attention to the color before.
Example from blackberryfaq.com, 8700 Dimension Today theme (a default theme):
