I hope to turn your idea into a living application.
From what is written in your description, you require an app that allows user to interact with the screen and get colour feedbacks.
For example :
1) User tap on screen with finger/palm (Tap)
2) The area being tapped will be drawn and filled with colour based on a colour picker maybe at the top of the screen
3) While the tapped area is coloured by the user's chosen colour, the rest of the area is filled with black/white(blank)
That is what I infer from your description. Maybe a comfortable timing will be 1-2 weeks
We can look into this for further discussion.
Thanks and hope to hear from you soon,
Best Regards,
Lawrence