If you are doing it as a way of formatting the page and still offering an option or button that allows the user to see the rest of the text, then it is not the same thing that you are thinking of in regards to Google. Google states that you should not hide text on the page to purposely try and trick the search engine.
In E-Commerce situations it is very common to hide part of the text, for instance when you have 4 tabs for "description, features, specification, colors, etc." it is a good idea to use a 'display: none' so that all 3 of the tabs are not shown all the time. This is not considered Black Hat, it is considered good design.
Matt Cutts has said quite a few times, if it is good for the user it is good for Google.
It is when you intentionally hide a block of text on the page with no way for the user to view it that you are using Black Hat technique.