In optics, chromatic aberration (CA, also called achromatism or chromatic distortion) is a type of distortion in which there is a failure of a lens to focus all colors to the same convergence point. It occurs because lenses have a different refractive index for different wavelengths of light (the dispersion of the lens). The refractive index decreases with increasing wavelength.
Chromatic aberration manifests itself as "fringes" of color along boundaries that separate dark and bright parts of the image, because each color in the optical spectrum cannot be focused at a single common point. Since the focal length f of a lens is dependent on the refractive index n, different wavelengths of light will be focused on different positions.
Thank you. I have a Hensoldt 6-24x72 and have had it for a couple of years. I've probably put 500 rounds under it, 100 from my 30-378, and I never noticed that, but then I wasn't looking for it either - I didn't know what it was. My turret indicator lines line up perfectly with the turret value lines.