Switch component with "disabled={true}" is greyed out this is not following the material design guideline colors.

• The issue is present in the latest release.
• I have searched the issues of this repository and believe that this is not a duplicate.

Current Behavior 😯

In Material UI disabled switches are greyed out

Expected Behavior 🤔

It should follow current material design guideline and use a dimmed out color which is much more readable

Steps to Reproduce 🕹

Steps:

1. Open code sandbox https://codesandbox.io/s/material-ui-issue-forked-w85sm?file=/src/Demo.js
2. The switches are disabled and greyed out.
3. Try to guess which one is checked...

Context 🔦

Using grey color for disabled switches makes it very difficult to distinguish checked vs unchecked status only the position switch remains to make a distinction.