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.
Bone marrow and thymus are also important parts of the lymphatic system. The lymphocytes and white blood cells contained in the lymph that help in the proper functioning of the immune system are produced in the bone marrow and thymus.