Hi rogue64,
thank's for your question!
A one-color game is something like this. You will need to pick-up a standard color (for example green) and then use different shades of it to reorganize different objects in a game.
A game-in-game game should be (for example) a small game that contains a bigger mini-game, or you can make a completely different game, but it needs to be describable by saying "it's a game-in-game game" or "it's something like game-in-game".
Please have in mind that if you didn't get anything you can always contact me.
Also please have in mind that anyone from these themes doesn't have to be selected and that more information will be released as soon as this jam starts.
Good luck and have fun!