Pong,
As you have indicated before, you don't particuarly care if your color is off, you like to make up your own. However, if you decide to go in your own direction, you should at least follow some rules of color harmony, that is, analogous color or complementary color. If you were using, for example, complementary color, your background should be a dull blue color to harmonize with the very bright orange of the face. If you were using analogous color, the background would be a warmer dull yellow instead of the yellow-green you have there now.
I would check out technical painting manuals as to the dangers of oil paint on paper. Even though many well known artists did that, they were meant to be only sketches. Many have not survived, and the few that have, have been lovingly cared for in museums. Ralph Mayer's,
"The Artists Handbook", is a good source.
Sincerely,