Adding color to hand rendered animation (Must Use Photoshop and Graphics Tablet)

I have a rotoscoped animation that I need colored in. This will not be full color for each frame, only a bit of color. (hair, shirts, eyes) for each frame. It will also only use 3 shades of grey to color in the world This will need to be done on a graphics tablet, and I have about 10000 frames to color (frame by frame) You will need to use the brush tool in photoshop, and color over the sections of the frames that I need to be colored in. Must be able to work full time Also, please see example image of a single frame needed to be colored in. In this image tree leaves and Jeep would need coloring. Tree leaves light grey, jeep dark grey, wheels very dark grey.