Site wide font family
Available styles:
body, html {
font-family: "Tahoma","Lucida Grande", "Verdana";
color: #333; /** OW_Control type:color, section:2. Colors, key:textColor, label: - Text **/
font-size: 13px;
line-height: 18px;
height: 100%;
min-width: 1000px;}
Keep on mind that Oxwall is not one huge piece of code. It is build of smaller components. Which makes the software incredible flexible. And you can assign certain font color to certain component separately. Depending on where you wish to change the font color, you might want to edit either language keys, or other custom CSS.
Please specify areas where you wish to change the color so that me and other community members can give some directions.
At this moment your question is way too general and there could be a hundreds of possible answers especially if you are referring to whether users themselves can select font color when they add blog post or something else. Please provide more information.