Forum post formatting...

[RealityRipple]

They are legible, but definitely reduced legibility.
Of course you can work around that with a background if you insist

Maybe it's my computer screens or my glasses, but the shades of red and blue both physically hurt to look at on the background's gray.

[Moonchild]

Fully saturated primary colours will always have that effect on dark themes, regardless. it's kind of inherent to how most screens handle the display of colour. Especially if you are using specific flat panels that will happily burn out your retinas with bright and harsh LED light. Often also exacerbated by poorly configured screens; toning down your brightness and contrast setting when using dark environments can make a big difference.
Just underlines my statements of using it sparingly. it helps keeping in mind dark backgrounds if you do.
Unfortunately dark themes are simply always going to be more problematic than light ones because of the contrast.