By definition a het looks no different than a normal. there are some gets that some people say have indicators (het pieds) but there is nothing 100%.

There are only 2 ways to know and only 1 works 100% of the time.

1. knowing what the parents were (doesn't always work *50% het x normal pairing is an example where this doesn't tell you for sure*)

2. breeding to a visual or a verified 100% het of the morph will always work.