A few days after the release of Safari 5.0, some users noticed that Mail messages generated by scripts and other applications would have the main body contents be displayed with a black background. We were notified by a reader and we found a small workaround, and Apple has since recognized this problem.
The problem is a rather simple one: with the latest Safari update, some error or oversight in the WebKit engine or Mail application now results in the HTML generation process for messages using rgb(0,0,0) as the value for the CSS "background-color" property for messages.
After our initial report on the issue, Apple seems to have acknowledged the problem by today releasing a knowledgebase article that outlines the fix we came up with several days ago, which is to use the "Make Plain Text" feature of Mail to strip out the HTML formatting for these messages.
Apple's article contains another option that will preserve text styles, links, and other formatting of the message body, which may be a better option for people who would like to preserve their message's links and other special formatting:
Click the message body
Press Command-A to select everything
Press Command-X to cut the selection contents
Press the delete key to remove remaining items
Press Option-Shift-Command-V to paste the contents back with matching style.
The suggestions so far for this problem are mere workarounds, but the problem is definitely recognized by Apple and hopefully will soon be addressed in an update to WebKit, Mail, or another component of the message-generating procedure.