Alpha change causes color drift

[jsthon]

Hi, thanks for the awesome work on this library!

I’ve noticed that when setting a color like rgb(17, 17, 17) or #111111, changing the alpha to 0.5 results in the RGB values becoming rgba(18, 18, 18, 0.5) or #12121280, which slightly alters the original color.

This makes it hard to preserve exact colors when only adjusting transparency.

Would be great if this could be addressed.

Thank you very much!