Palettes: Difficult To Distinguish Disabled Search Box From Enabled Search Box

The following issue was reproduced in revision 546fcee.
1. Launch Musescore
2. Change to the Dark theme
3. Open a score
4. Look at the Search box in the Palettes panel. (Add palettes button.png)
5. Play music
6. Look at the Search box in the Palettes panel. (Playing Music.png)

The Search box looks more enabled than normal when music is playing (and the box is disabled) because the word "Search" lights up. Under normal circumstances, the Search box looks grayed out. This is probably not the desired outcome.