how can i change the default header on my widgets?

A couple of the widgets I’m using have a header on them and I want to change it, or at least change it’s appearance. If you go to my site http://www.spencerteeter.com and look at the “Twitter” and “Gallery” widgets near the bottom of my sidebar you’ll see the grey header bar on them. I either want to

a)remove it, or
b) change its color to black.

my theme is mystique

Any ideas?