CSS variables in color data attributes work!

[0str1ch]

Using standard CSS variables var(--your-varible-name) in the primary and secondary data attributes works.

Might be helpful to include this tip in the documentation as it makes swapping colors globally for icons in a non-destructive manner possible, without editing the Vivid Icon source in node_modules/vivid-icon/src/config.js and then rebuilding from source every time a change is made.

Example for those unfamiliar with CSS variables:
<i data-vi="flame" data-vi-size="90" data-vi-primary="var(--primary)" data-vi-accent="var(--secondary)" data-vi-prop="var(--tertiary)"></i>

Then, set up your variables:
:root { --primary: #010101; --secondary: #333; --tertiary: #dbdbdb; }

And that's it! Hope this helps someone.