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I've never heard of a "penalty" for invisible text, as in a lower ranking. You just get flat-out banned, and you would know that right away when the traffic vanished from the SE that banned your site. I have heard of the occasional accidental banning because an algo didn't recognize that there was a table background color, but nothing recently.
Nearly every site has invisible text by some definition. E.g., this site says above in white letters, "Discussion: avoiding invisible text
Is a similar background color and text going to get me penalized?"
Well, there is white text, and the background of this page is FFFFFF, so there you go, this site should be banned. Of course we know it's in a table cel set to a dark blue color, but the search engine doesn't know that. There's no way their HTML parsers are so sophisticated. And even if they were, what if you had a graphical background to the page? Will the engine load the graphic then do a color analysis on it? Where will it end?
My position is this: the search engines have a job to accurately reflect what the HTML authoring community is doing. As a web author it's not your duty to conform to what the search engines want of you. If they want to play little games like banning certain practices, that's their business, but ultimately it's we who determine their habits, not vice versa.
Bolot