Bug Report

• Package version(s): 6.189.4

Priorities and help requested (not applicable if asking question):

Are you willing to submit a PR to fix? (Yes, No)

Requested priority: (Blocking, High, Normal, Low)

Products/sites affected: (if applicable)

Describe the issue:

We'd like to use semantic slots to style disabled text for the ActionButton. However, the current implementation seems to use neutralTertiary.

https://github.com/OfficeDev/office-ui-fabric-react/blob/6ff7873e60436513ce7c3e4f39982a461fa5c86f/packages/office-ui-fabric-react/src/components/Button/ActionButton/ActionButton.styles.ts#L47

Actual behavior:

See codepen and notice the button is not red.

Expected behavior:

The button should be red assuming one of the suggested semantic slots is appropriate.

If applicable, please provide a codepen repro:

See https://codepen.io/anon/pen/jjEVjw

Thanks - please let me know if I'm missing something.