Why does the white font color only apply to normal text body and not the rest of the dark paragraph styles, do I need to change the Paragraph style to white/light to be able to use it?
Seems you assume standard colors are used so it is just a matter of redefining the pallet for dark mode. Apparently not: 149934 – Constant Colors Fail WCAG 2.1 Contrast Ratio so every color used will need to be redefined. Dark Mode is very much an early release.
You didn’t mention OS name, LO version nor save format. Please edit your question.
By default, all paragraph styles have their font colour set to Automatic. This means Writer will select black (commonly) or white when it detects the paragraph background, so that there is maximum contrast between foreground and background to make text readable.
This simple algorithm is defeated with some fancy background colours.
Dark Mode is a rather recent feature, pushed in by the favour it has in the game business (but it is a definite ergonomics fault in office environment). It impacts many aspects of rendering and these secondary effects are not well understood and hence tamed.
If you can, don’t enable dark mode. Instead, define your own colour scheme through styles (page, paragraph and character styles) and application colours for the screen area not part of the document.