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. The lymphatic system is part of the immune system. It is made up of lymph nodes that trap microbes, and the spleen (a blood-filtering organ). Lymphocytes are also found in the lymphatic system.