Since not everyone will be able to get this feature to work with their lighting I thought what if the circle was backlit?
Well, I already tested this and it works perfectly.
Full screen tumblr and click on the circle so the lightbox activates which will black out the rest of the screen. There will be enough brightness and contrast for the 3DS to easily recognize the circle and open gates. You can use the static red one or later (since the game said something about “different color circles making different gates) I made a very slow moving gif with a whole rainbow of colors to try. It’s slow moving so you should be able to have enough time to pick a color (and no one will get seizures).