Aaron, you can't have a gecko het for SHTCTB. The term het only applies to recessive traits, which would be all the albino strains, jungles/stripes, blizzards, and patternless. Every other morph is line-bred, which means that both of the parents need to have certain characteristics and (ideally) be closely related in order to have offspring that are more likely to express and perhaps improve those characteristics.
As far as the percentages, they refer to the possiblity of a het. 50% het means there's a 50% chance of them being het. Basically, there can be different combinations of traits that can get passed down to the children, so it's hard to tell which babies are born possessing het traits if just one of the parents was het, because, well, it's het. You can't see it. The only way to prove it is to breed them.
Ohohoh, funny story. In my high school biology class, in order to explain genetics, my teacher arranged a project where we got paired up boy-girl. The point was to compare our physical features to determine what our children would look like, and then we had to draw a picture of our predicted children. I'm Chinese, and I got paired up with this redhead kid. Neither of us took the project seriously when we drew our daughter, and we ended up having the ugliest kid you could imagine! She had darkish hair, freckles, a pignose, braces...
I blamed it on the redhead kid.