I usually paint the white using a mix of white with a little blue added (just enough to create an off-white color). Depending on the scale of the figure, I then either paint in the iris with a small (20/0 or smaller) brush or use a colored drafting pen (available at art supply stores and office supply stores). Finally I use a black drafting pen for the pupils. You may also find it easier to paint the eyes by having the figure look slightly to one side rather than straight ahead.
As far as the lips, I highly recommend the use of oil paints for this. I currently mix red with a little white and some blue and then use a small brush (again 20/0 or smaller) to apply the paint. Finally, I wipe the lips off with a brush or clean paper towell to blend the color in
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