A problem that arises in high contrast photography is purple fringing due to short wavelength light being refracted around a dark/bright transition. This is different from chromatic aberration of the lens which results in green/purple fringing at such transitions. The latter can be largely removed by resizing the red and blue channels. The classical fix for pure purple fringing has been to use Darla’s Purple Fringe script for the GIMP, but the results are rather modest and require fiddling with afterwards, as shown in these two images:
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