This is most likely moiré/aliasing, not lens chromatic aberration. Wound guitar strings have a very fine repeating pattern, and when that pattern interacts with the camera sensor’s pixel grid—especially on cameras with weak or no anti-aliasing filter—you can get false color artifacts.

A practical fix is to use moiré reduction in post-processing. In the original case, Lightroom’s moiré reduction tool removed the issue successfully.

If you need a capture-side workaround and the subject/camera are perfectly still, another method is to photograph separate red, green, and blue exposures and combine them later. That can suppress aliasing, but it is more complex and only works for a stable setup.

So the short answer: the strings’ fine structure is creating moiré on the sensor, and the easiest solution is moiré correction in post.