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 closely related to the blood cell-forming system. White cells called lymphocytes are found in the lymph nodes (small oval-shaped organs found throughout the body that help trap and kill disease and infection that invade our bodies).