Color contrast question - button background

Hi there,



I have a question about button color contrast.



I am familiar with success criterion *1.4.3 Contrast (Minimum):* The visual
presentation of text <http://www.w3.org/TR/WCAG20/#textdef> and images of
text <http://www.w3.org/TR/WCAG20/#images-of-textdef> with a contrast ratio
<http://www.w3.org/TR/WCAG20/#contrast-ratiodef> of at least 4.5:1, for
normal text.



However I have been told by colleagues recently that there is also a
requirement for button color contrast  with the background that it is
placed on.



If there is insufficient color contrast using 4.5:1 between a button and
its background , would this be considered an accessibility failure? Or is
text and background colour sufficient?



If there is a requirement, is there any instruction that would apply it to
some buttons and not others, or should it be applied to all on a site?


Any advice or guidance would be much appreciated.


Thanks,

Aleta