We use Bootstrap 4 which is completely WCAG 2.0 compatible. Color contrasting will be subjective to your background color. You likely need to make the background color darker. Does hovering a row allow it to be more visible for you? We do not apply a background color in backend so it's subjective to whatever your backend Joomla template is using which maybe why there's contrasting issues since it's not being reset by Bootstrap.

Will review adding an option to CB to select a backend template (at this time it forces default), which would allow custom templates generated by CB Template Changer to apply to backend. Regarding CSS overrides no they do not load in backend as it typically causes too many odd conflicts.

forge.joomlapolis.com/issues/7384

Below are the Bootstrap 4 colors.

getbootstrap.com/docs/4.1/utilities/colors/

In addition to their accessibility note regarding color contrasts.

getbootstrap.com/docs/4.1/getting-started/accessibility/#color-contrast

With that said the color choice for the Registered usergroup in the Groups column doesn't really make much sense. Have added a feature ticket to change it to a different Bootstrap 4 color.

forge.joomlapolis.com/issues/7385

Install from web is misplaced in IE11. It shows to the div.
Unfortunately, at this time IE 11 is the only browser thaat fully supports ZoomText, Supernova and similar magnifying software used people with low vision.

IE11 does not 100% support flexbox so you may or may not have some layout issues like this. There's not much we can do about it as it's a limitation of the styling engine, but have added a note to take a look.

forge.joomlapolis.com/issues/7386

Just curious, why is Registered set to text.warning color?

Don't particularly know. Just how its always been styled going as far back as CB 1.x. Should ideally be green (text-success) or not colored at all.