Color schemes (luminance modes) and color themes (aesthetic styles) are not the same thing. Halloween theme can have light and dark schemes.

Also, prefers-contrast media query exists, which can be used in combination with the luminance modes (color-scheme): halloween-light, halloween-dark, halloween-light-high-contrast, halloween-dark-high-contrast.

https://news.ycombinator.com/item?id=47832705