HTML_FONT_LOW_CONTRAST

The official SpamAssassin description for HTML_FONT_LOW_CONTRAST reads:

HTML font color similar or identical to background

Well, that's not particularly helpful, now is it?

99% of the time, this issue is being raised because SpamAssassin's contrast sensor is not smart enough to detect missing background styles. Put another way: if you've got a blackdiv and whitetext inside that div, be sure to declare the whitetext as having a background color; otherwise, SA assumes that it's white on white, and therefore low-contrast.