You probably shouldn't be coloring while onion skin or outlines are on. That would make things incredibly difficult if not impossible to color.
If you are painting the fills with a brush, you need to be able to see where you have drawn them before.
Thats Why i have onion skin on, but i am unable to se anythinG drawn with a brush on the previous frame. (Or next frame)
Is it the color of the Onion Skin that's making it hard for you to see? You can change the Onion Skin color by going to Edit>Preferences... Try white or black instead of a color.