Build in accessibility during the visual design phase.

Graphic designers should work closely with accessibility /508 experts before implementing a design into a website. Some accessibility issues can be avoided or/and fixed early during the visual design phase. For example, some of the principals that should be considered to make a design accessible are: Color contrast, use of CAPS, font size, heading structure, reading order, form controls.

A great related resource: http://webaim.org/resources/designers/#infographic