@Background Pony #FB9C
It’s an effect called chromatic aberration. Some artists will do it to mimic the blurring effect in photography as a stylistic choice. There’s several ways to do it like brush settings or layer effects. Based on the sparkles (a brush I recognize in CSP) and some areas (like in the corners or along some lines), I think it’s done through a filter or a brush effect afterwards, I guess the latter.
It can help create a quick effect to form interest in the image that would otherwise have all flat colors. If you zoom in on it, it’ll look strange but those tiny lines will make a huge impact on the composition of the whole image. This is because our eyes are built to notice certain details and it’s easy for them to glaze over the image. But having sharp, subtle changes can make the picture “pop” better so the eyes have details to more easily focus on.
Nnaly seems to do it a lot on close-up portraits or images involving the princesses when strong lighting effects or complexity of items/accessories aren’t present.
Novice question, Looked at the zoomed image, the black lines have red and then yellow above them and blue below them. Is this a technique, or standard software effect built in, what is it exactly?

your current filter.Edited
Amazing answer, thank you
It’s an effect called chromatic aberration. Some artists will do it to mimic the blurring effect in photography as a stylistic choice. There’s several ways to do it like brush settings or layer effects. Based on the sparkles (a brush I recognize in CSP) and some areas (like in the corners or along some lines), I think it’s done through a filter or a brush effect afterwards, I guess the latter.