Quick run down on some controls hidden in the game:

Chat:
Ctrl + T - Opens up chat window. Only works in drawing screen, waiting screen, and presentation screen
Red rectangle closes the chat window

Drawing Screen:
Don't see the color you want? Right click on any color to replace it!
Ctrl + Z - undo
Ctrl + X - Eraser
Ctrl + C - Fill bucket
Ctrl + V - Brush
Numbers cycle through the color palette, cycling through the colors will retain current tool if it's a brush or bucket. If you select a color and the eraser is selected, the brush tool will be auto selected.
Ctrl + Number - Cycle to color + select brush tool