Have you played with ATO->Widgets->Widget List Items
Note that changing these will effect all widgets. If you just want to effect the pages widget put this in ATO->HTML/CSS INSERTS->CSS Inserts
HTML Code:
.widget_pages ul li a:link,
.widget_pages ul li a:visited,
.widget_pages ul li a:active {
padding: 0 0 0 5px;
color: #000000;
font-weight: bold;
border-left: solid 7px #000000;
The 'color: #000000;' says it will be black