In the final release of WCAG 2, the acceptable minimum color contrast ratio was changed from
4.5:1. I’ve updated both my color contrast tests — Color Contrast Comparison Tool and the Color Contrast Spectrum Tool to reflect the change in contrast ratio.
What does this change mean?
Essentially, this means that the working group decided that color combinations with lower contrast (more similar colors) were acceptable for general use on the web. This is certainly good news for designers, since it will provide for a greater variety design voices than previously.
The contrast ratio of 4.5:1 was chosen for level AA because it compensated for the loss in contrast sensitivity usually experienced by users with vision loss equivalent to approximately 20/40 vision. (20/40 calculates to approximately 4.5:1.) 20/40 is commonly reported as typical visual acuity of elders at roughly age 80.
Understanding WCAG 2.0; Understanding Success Criterion 1.4.3
While the previous higher ratio requirement may have accommodated for an even larger audience, the decision of the committee appears to have been that it had crossed a line of diminishing returns, and that the lower requirement is sufficient for most common use.
This effects the minimum ratio to accommodate at Level AA, and the minimum ratio to accommodate at Level AAA for large print.
Still — don’t get carried away!