Yes, a het animal carries the gene for a trait but does not show it in its appearance.
Simple recessive genes require two copies of the recessive gene to be present in order for the trait to appear. A snake that is het for a trait is one that carries one copy of the gene. It expresses the normal version of that gene (normal is typically dominant rather than recessive). Offspring from it have a 50% chance of getting the recessive vs the normal version of the gene.
It is not possible to say what color a het animal will be because it depends on other genes it expresses. You can have a normal appearing corn that is het for snow (het for both amel and anery) and it will have the normal corn colors. You can have an amel (albino) corn that is het for snow (het for anery in this case) and it will appear to be an amel.
hope that helps a bit - there are lots of genetic sites on snake morphs that can provide more detail,