Can the default colors for the gemini http site be changed?

[zephryn]

 > For contrasts, there is apparently a "prefer-contrast" media query
 > parameter which can be used by clients to signal their preference.

I think that using what you mentioned (prefers-contrast) along with
prefers-color-scheme should definitely be considered! The former is
still pretty experimental, but both could help web clients have a bit of 
choice without having any scripting involved.

~zeph