I think you can harmonize fully saturated colors too, it's more about the distance that they are apart that makes them clash. Pip's nose color in the background will look milder even though it's just as saturated as the dark blue, but it's closer in tone to the green ground. I always try to avoid using maxed out RGB and CMY colors as fills, they have too strong of a visual impact. People had ray-tube televisions back in the day of the Sega Master System and the colors got washed out by how they were displayed and the distance that players sat from the screen. What we see on our modern monitors is very different from what highly saturated colors used to look like.