Is it permissible to wear a loose garment that has a pattern resembling leopard or tiger skin, but with colors that are not striking and different from the known colors of tiger skin?

That which is an adornment in itself is forbidden for a woman to wear, and this is determined by custom. If these colors are not eye-catching, such that they are not considered an adornment in the custom of the people in your country, then you are permitted to wear them.