Pixel Art: "Darker border" when using Replace Colour feature

[Boot]

I am working on a pixel art project on Pixelmator Pro.

When using the Replace Colour feature on pixel part, it works as advertised for the most part – but it does create some visual artefact around the border of the colour. In this example, I changed the yellow to green, and you can see that the mutated colour has a border around it. (Zoom in, the border surrounding the "green" is now darker. How can I replace colour without introducing such an issue?

Are there any plausible workaround?

[EllenM]

There seems some smoothing involved with the color replacement tool.
I´d suggest the Color Fill tool with disabled "Smooth edges" and a click+short-drag=0% Tolerance fill instead of just click.

[Andrius]

Yeah, Replace Color is currently optimized for replacing colors in photographic images, where you want nice smooth edges and anti-aliasing. Here, that's obviously less than ideal. Just like EllenM said, using the Color Fill tool is one option – if you want some more control, you could try using Edit > Select Color Range, which also has the option to turn off edge smoothing. Then you can create a shape from that selection, fill it with color on a new layer, and more.