I found this site: http://www.doityourself.com/stry/tidecoldwaterqna I don't know who wrote all the answers, but apparently Coldwater Detergent does save your clothing's color.

Good job. I only read that, but haven't checked if that's true, that washing with cold instead of warm water saves as much energy as running a dryer uses; but while drying lines are becoming finally a little more popular in the US, there really doesn't seem to be much about cold-water detergent. Do you know if "normal" detergent really doesn't work well in cold water?