Bug report

For some backgrounds mdc-theme calculate incorrect ink color.

Ink color for background color is usually chooses using this algorithm:
https://www.w3.org/TR/UNDERSTANDING-WCAG20/visual-audio-contrast-contrast.html
https://www.w3.org/TR/2008/REC-WCAG20-20081211/#relativeluminancedef

But here there is a condition that give priority to white ink color if both white and black are suitable according minimal contrast criteria.

That's why for background #018786 (secondary variant color from base theme) white ink color is white, but contrast for black ink is higher (black has 4.8111258691 white has 4.3648826847). Moreover contrast for white is lower that required contrast for small texts.

Color selection tool offer black ink for this background.

Steps to reproduce

1. Set secondary color to #018786
2. run npm start (or open demo page)
3. Go to fab button demo
4. Buttons will have white ink color

Actual behavior

Buttons have white ink color.

Expected behavior

Buttons have black ink color.

Possible solution

Remove this condition ($lightContrast < $minimumContrast) from theme component or at least update 3.1 -> 4.5 (4.5 is minimum required contrast for small texts).