Do you have a link to that guideline? I know there are a bunch about allowing users to override whatever the webdesigner specifies, and about having sensible contrast.
WCAG 2.0 level AA requires a contrast ratio of 4.5:1 for normal text (14 point and bold or larger) and 3:1 for large text (18 point or larger). Level AAA requires a contrast ratio of 7:1 for normal text and 4.5:1 for large text.