[plt-scheme] MrEd: Background color of text-field% with password style

Hello,

I've noticed that the password style text-field has a fancy grey  
background instead of bullets (at least on OS X). That's really good.  
Now I wonder whether it is possible to change the color of this  
background programmatically. I was thinking about using it to visually  
indicate the password quality (red<yellow<green).

Is that possible?

Best,

Erich