light yellow to dark brown, orange, red, white; occasionally greenish or bluish due to fluorescence
Specific gravity is a key indicator, one which may be tested by placing the specimen in a saturated salt solution having a specific gravity of approximately 1.12-1.13, in which amber should float. Plastic imitations, in contrast, will typically be denser and thus sink in a salt solution. Other tests for amber (versus plastic) include a hot needle test (checking for distinctive odor), sectility (scraping with a knife to see if it chips or crumbles instead of curling).
Amber is essentially a fossilized plant resin, often with fascinating inclusions. The presence of, amounts, and kinds of trapped material, such as insects or air bubbles, can cause the specific gravity to vary. Copal is an immature(young) version of the same material.