there’s no way to color on a video in real time in Photoshop,, but what you can do is bring the video into AE go to Composition>Add to Render Queue and in the RenderQueue window click on OutputModule then choose to export it as a filmstrip rather than a Quicktime.
What you will wind up with is a .flm which is basically every frame of your video lined up on a single image. Then bring it into photoshop and scribble on it to your hearts content. You can even do simple animations, for instance, if you want a wiggly line in your video, draw a line down the film strip. Be sure that when you’re done you save it in it’s original .flm format.
Now here’s the cool thing,, you can bring the .flm image into AE and it plays it like a video! The drawings on top will be jumpy and jittery, so this technique is great for scribbles. Just export it as a quicktime when you’re done.
*Note:You may want to change the frame rate of the original comp so the filmstrip doesn’t have too many images
This technique is also great for adding noise and grain to create an old time movie effect, or for applying PS filters that AE doesn’t have.