My mother in-law said the blue black and green mark is caused by wearing socks. Is that true? I am worried because I feel that wearing socks is important especially when baby is sleeping in aircon room or with fan on. His feet tend to become cold easily. My son is 4 months old..

Most babies have cold hands and feet as the rest of their body develops. Cold feet should only be addressed as an issue if the baby have signs of vomiting, high fever or shortness of breath. http://www.livestrong.com/article/513496-why-does-my-infant-have-cold-feet/

Infant sleeping bags are useful as well. That way, you don't have to put socks on him but his feet will be warm.

If you are worried, you can let your baby wear long pant that covered up to the toes.

thanks