The CMY colours (commonly mistaken for Blue, Red and Yellow) are the answer when printing as mixing any two will form one of the darker RGB colours. The mix of all three CMY colours creates Black, although in practice this is very muddy.
White blood cells, like all blood cells are created in the bone marrow from certain stem cells. However, some lymphocytes are created but undeveloped or immature.
The lymphatic system is part of the immune system. It consists of a network of vessels that carry a fluid called lymph, similar to the way that the network of blood vessels carry blood throughout the body. Lymph contains white blood cells called lymphocytes that are also present in blood and tissues.