Allow spaces theme color to be much much darker

[Ralms]

Hi there,

I just started using Zen and so far I'm freaking loving it.
Specially the idea of spaces (I just hope they also provide better memory management, as I tend to have hundreds of tabs open lol), however, there was something that I wish was better.

I'm on Ubuntu 22 (due to work restrictions) and when defining a theme color for a space, I've noticed 2 things:

1. Color wheel doesn't show up, I have the cursor but move it blindly, maybe a bug, don't know.
2. The contrast slider doesn't allow colors to be dark enough.

This request is specifically regarding point nr 2, color shades, as right now, when I pick a color, even with the slider all the way to the left is still way too bright.
Which is a problem for 2 reasons:

1. I prefer darker themes as its easier on the eyes.
2. As dark theme is enabled, the fonts remain white, resulting in being harder to read text when applying color as a theme.

Would be great if the contrast slider (or brightness or saturation slider, I don't know the name), would allow fairly dark colors, so that we essentially have a shaded dark theme.
If I would evaluate the current brightness, where all the way to the right is 100%, I would say that all the way to the left currently is around 30%.

Thank you.