I think I see what he's talking about. Go to 3-3, Shifty Boo Mansion. Since a lot of the stage background is pure black, I can see the blue tint along the left and right edges of the gamepad screen and TV screen.
If you go to 3-4, Pretty Plaza Panic, I can see sort of a yellowish/white tint on the left and right sides.
I have a feeling that's there by design, possibly an effect to increase the visual mood of the stage? Or maybe it's supposed to give you a subtle feeling of looking into the "distant horizon", kind of like how distant objects appear bluish?
This effect doesn't seem to appear in every stage, though. 3-5, Pipeline Lagoon doesn't appear to have any side tinting, even when you come across a pure black wall.
Edit: Now that I play through 3-3 again, it's possible the blue tint on the sides were added to match the blue tint of the ghosts when they chase you, making you feel like you're surrounded by this spooky aura while you're in the ghost house.