My 5 year old son has a little yellowish hands. Also for last few weeks he sometimes complains of tummy aches, just around dinner time. Any suggestion?

Check his diet. Sometimes slight yellow to orange discoloration can indicate too many yellow/orange vegetables and is a harmless condition called carotenemia. Tummy aches around dinner time could be behavioral or he might need a snack a little earlier before dinner as could be "hunger pains". Constipation is a consideration also. A visit with your pediatrician for more info can be helpful.
Abdominal Pain. Aside from caroteinemia for the yellow discoloration, make sure the abdominal pain is not from plumbism. We still check lead level until 5 years old.