So I can make ANY game I want? Even a coloring game????

Yes

Yes, you can make ANY game because this is only a personal challenge to get you to your own schedule.
For example, Every day start making a mechanic for your game

or Make a new tool for your game (if you are making a coloring game)

This may just be my interpretation of it, but the "dev" in DEVtober to me is about developing. I'm using this month to develop some skills and am more than 100% sure I won't actually be able to make a playable game. Instead, I'm focusing on just doing tutorials in Unreal and Blender for the entire month, just to keep learning and keep developing as a creative.

So yeah, make whatever you want as long as you can find a way to do a little bit every day (which is the biggest challenge to be honest).