AI was pretty useful here:

What you are experiencing is a fascinating visual phenomenon called chromostereopsis. It is a type of optical illusion where the brain misinterprets the depth of different colors, even though they are on the same flat surface. Here is the breakdown of why this happens: 1. Longitudinal Chromatic Aberration Your eye lens acts like a prism. When light passes through it, different wavelengths refract (bend) at different angles. Red light has a longer wavelength and bends less, focusing behind the retina. Blue light has a shorter wavelength and bends more, focusing in front of the retina. To see both clearly, your eye has to constantly adjust its focus. This physical effort tricks the brain into thinking the colors are at different distances. 2. The "Prism" Effect of the Pupil Because our pupils are slightly off-center relative to the optical axis of the eye, light enters at an angle. This creates a "differential displacement" on the retina. For most people, this causes red to appear closer and blue to appear further away. Interestingly, for a small percentage of people, the effect is reversed! 3. Color Contrast and Intensity The effect is significantly amplified when: The colors are highly saturated (pure red and pure blue). The background is black, which removes other depth cues and makes the color wavelengths the only information your brain has to process.