I just got a chroma key blue background but haven't had time to try it. I have heard that using this type of background can cause a color cast to appear on the subject. Has anyone had this happen. Any other advise on using the chroma background would be appreciated too. Thanks

Any color bg will cause a color cast on your subject if they are close enough to it, simply from the reflected light (much like a colored wall will reflect a color cast).

I've never worked with chromakey, and am not quite sure how it would serve any purpose in still photography (subjects can be "extracted" easily with any color bg), but I would say to get the best results, make sure it's lit evenly and the subject is far enough in front that the color cast doesn't reach them...