The WPT test, https://github.com/web-platform-tests/wpt/blob/39c4da44b6/css/css-color/parsing/color-invalid-color-mix-function.html, currently requires that a color-mix() function with all 0% percentages, like color-mix(red 0%, blue 0%) is invalid and should fail to parse.

I believe this is because prior versions of the spec included the text "If the percentages sum to zero, the function is invalid".

I don't think the current version of the spec has any such requirement, but I wanted to double check first before removing those tests.

cc @svgeesus