Outline fonts are used for their ease of scalability. Color - stimulation of the eye by various lengths of lightwaves. Proper use of fonts, or typestyles can make words easier to read or convey a feeling. Using browser safe fonts is suggested to ensure proper display of your type so that they will display properly in both Windows and Mac platforms. Adding these fonts with CSS will allow the browser to choose from a list as well as decrease your file size.
Color saves the viewer from thinking too much.
It breaks the page into useful chunks and creates a system. The eye automatically treats similar objects as reacting the same. For instance, on this page each heading is highlighted in red. The viewer knows automatically that when they see red it is the title and the beginning of a new thought. If red words were placed randomly in the paragraphs it would be very confusing and the system would be inconsistent.