When we had Silly Putty all over the place I did an internet search on something like "silly putty stain removal" and discovered entire websites dedicated to this type of thing...unfortunately, I never bookmarked them, since I figured I'd just do another search if I needed. So, some sort of netscape search(or whatever your preferred search engine) would probably turn up some advice.
Anyway, the package says to remove as much as possible, let dry then vaccum. After it's dry you might try a stiff handwhisk broom and see if you can sweep some of it out (that way the beaters on your vacuum won't pound so much of it into the carpet). Sweep it right into a dustpan.
Test anything you do (including sweeping) in a small area first.
Water turns playdough into a vile mess. I'd avoid wetting the area.
OTOH, when dd colored all over the brand new (as in 2 days old) carpet the people who came to clean it suggested that you can clean some stains out of light colored carpet with a mix of nonsudsing ammonia and borax. I've never tried it. This was years ago, so in the event that I've got the wrong 2 cleaning agents and am advising you to make some sort of toxic gas PLEASE check with Poison Control or somesuch to make sure this is a safe mixture!
We currently have hot pink on the sculpted Berber 2 feet from here...doesn't really impress me as a problem to get up, but it probably varies by carpet type. I figured I'd vacuum it eventually. Plus, having been through the Silly Putty incident this strikes me as small potatoes....