Human eyes don’t see most wavelengths in focus.
Because chromatic aberrations cause simple lenses to have different focal points for different colors, and the human eye is essentially a simple saltwater lens, it suffers from considerable aberrations. The focal plain is positioned near the red/green focal points, which overlap strongly, so most natural wavelengths are pretty close to focus. Blue however is not focused very nearby, so it is rendered permanently unfocused. The brain does a great job smoothing these issues out, such that it’s mostly only noticeable in the most obnoxious bright blue lights.rK3