Flushing in general can be caused by many things. From alcohol, to niacin, to anxiety, diabetes, too much vitamin C, hyperthyroid, polycythemia vera, adrenal problems, heart problems, opiate withdrawal, exercise and numerous other things.
There is a condition called Raynaulds syndrome or disorder. It is a condition where when a person is in the cold, or anxiety can bring it on, there is a vasoconstrictive reaction (usually in the extremities, but can occur on the nose or cheeks too) - this at first causes the skin and/or nail beds to look white or lighter than usual. This is often associated with pretty severe pain. In severe cases it can cause circulatory damage and necrosis. That is more rare though. Often though, when the contriction opens up, the hands flush red for awhile. There can be a stage where the hands appear purple or blue too.
So with your hands turning red, it indicate that for some reason your circulation is opening up and allowing more blood to flow to your hands. If you had any other symptoms along with this like swelling, it could indicate a problem with the veins - as the blood is being delivered and then not being carried back to the central circulation. This happens some times to people that have veins damaged or occluded for various reasons - in the elderly it can be from thrombosis, clotting and cholesterol.
Certain medications could cause circulatory changes like this to..
So you may want to pay attention and see if it is related to any supplements or medications you are taking, or anything else. If there is no pain or problems associated with it I would not worry to much. If it increases or other symptoms develop, then you may want to have a check up to make sure there is not a metabolic or other problem developing.