Those are really nice shades of purple…

But on their own, none of them read as the same color.

I think it might be because this purple is a non-spectral color.

According to some authors, purple does not have its own wavelength off light. -According to wikipedia

Apparently there is no real scientific consensus on what color purple really is and that alone is wild.

https://en.wikipedia.org/wiki/Line_of_purples