As long as the crock isn't red, yellow or orange I wouldn't worry about lead. It is a OHSA regulatory nightmare so I would assume that most american made crock pots, which seems to include most Crock-Pots, would be lead free. I wouldn't worry about it that case even if it was a suspect color.
If you want to be really sure you can always buy a home test kit for about $12 to swab the outside here is a consumer reports rundown of some options.
There are also cadmium test kits but I couldn't find any regulatory standards for these, thus they are probably more of a buyer beware sort of situation