How to tell if content is passed through t()?

I'm not sure how to determine whether content on my site can be found/replaced using this module. For instance, if I want to replace all instances of the word "black" with "white" throughout my site on pages I created--whose content I assume passes through t()--will this module do the trick?

I've tried doing the equivalent of that find/replace and it did not work. I've got the module set up just fine and I get the confirm message saying my changes have been "saved" but they don't take effect. I've tried clearing my cache, etc. but that doesn't change the results. I'm guessing that for some reason my content is not passing through t() but I'm not sure:

-why it's not
-how to determine if it is

Thanks very much for any help. I'd really love to get this working.