Mongolian spots are the pigmented birthmark(congenital dermal melanocytosis, green/blue/grey...). Some of the Asian babies with the higher percentages of presenting these harmless birthmarks on their backs, buttocks or elsewhere(more rarely/may link to metabolic disease). These birthmarks usually disappear by age 5, however, some people may live with them for life. The birthmark certainly is not caused by the painting behavior of the father!! Try to relax. Heathy lifestyle with proper nutrition, prenatal vitamin supplementation, reduced stress level, regular check ups, regular/suitable exercise and adequate sleep during pregnancy can really help smooth delivery of a healthy baby.