The styling will need to be looked into for changing. ::ng-deep might have to be used, which is deprecated. Other Material styling has already been looked into, and Google has not always made it easy to change. There might be a way in the top level styles.css. This wouldn't be the worst thing, as it would change all Mat button disable styling, which is what is needed.
Per Steve:
Need to change the style for disabled buttons. They are a bit hard to read because too faded. https://github.com/OpenWaterFoundation/owf-app-snodas-ng/issues/3#issuecomment-805633951
The styling will need to be looked into for changing.
::ng-deepmight have to be used, which is deprecated. Other Material styling has already been looked into, and Google has not always made it easy to change. There might be a way in the top level styles.css. This wouldn't be the worst thing, as it would change all Mat button disable styling, which is what is needed.