That skill of judging material by sound, did that translate to other parts of his work too? Like, could he just listen to a wall tap and know what was going on with it?

Consider how flat design works for people who have a hard time seeing screens. The super simple shapes and high contrast @the_casey mentioned can be a big help, but only if you really focus on clear icons and spacing. Maybe the goal isn't just looking warm or cold, but making sure it actually works for everyone trying to use it.