In the beta release, there are several options to change the appearance. Since they are still subject to change, they are not yet documented here (you can delve into the source more if you are curious). The full release version will have documentation for these features as well as API integration. I also plan to include an easy way to change the style template and include some different choices.
Skinning Jcrop is not currently supported.
However, if you are determined to alter the skin, it can be done. I'll assume that to do this you are savvy enough to not need instructions. If you plan to do this, I will give you some tips that will make the task easier.
If you mostly want to change colors, etc...it should work out ok. More drastic modifications might involve changing undocumented options or hacking the source. That's why I currently refer to skinning as an unsupported feature. It is possible, but it probably involves more headache than it's worth.