Mayo may not be able to, that's all stashed away in the CSS files.
It's well hidden in phpbbroot/templates/[template name]/[template name].css
something like /var/www/html/phpbb/templates/subSilver/subSilver.css
On my ancient phpbb2 install it's line 156 (for subSilver):
Code:
.quote {
font-family: Verdana, Arial, Helvetica, sans-serif; font-size: 11px; color: #444444; line-height: 125%;
background-color: #FAFAFA; border: #D1D7DC; border-style: solid;
border-left-width: 1px; border-top-width: 1px; border-right-width: 1px; border-bottom-width: 1px
}
Change whatever the value is where the #444444 is to something else more appealing.