I've been using the recolor tool extensively in Paint.Net v3, but now in v4 its logic seems to have changed, let me explain what I used to do:
- I have many images (PNGs) drawn in black, with antialiased borders over a transparent background. If I wanted to make a colorized version of one of them, I'll pick the recolor tool and select black as the color to replace, and then the new color I wanted (e.g. Red). If I set the tolerance to 0 and disabled anti-alias, it will replace all the black pixels with red, regardless of their alpha value (but maintaining it). That was very useful because now I have a picture colored in red, included the anti-aliased pixels which keep their aplha value.
- I cannot do this any more in v4, even though I tried several combinatios of settings: if there are pixels with alpha values, they don't get colored unless I increase the tolerance, and when they do, the replacement color is not the one I originally selected but a modified version of it (e.g. a darker red, but still with the alpha value).
I'm not sure if this behaviour is by design, or if there's a bug on the recolor logic. Anyway, let me know if you need further explanations or some sample images to test.