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.
Lymphocytes move around the body in lymphatic vessels that contain a milky white fluid called lymph. Lymphatic vessels connect lymph nodes throughout our bodies. The lymphatic vessels collect into large ducts, which empty into blood vessels. Lymphocytes enter the blood through these ducts.