I'm not sure if this is what you mean, but you want MX to show files you already have with a seperate color in the result list? to keep track of files you already have?
I've been looking for that feature, but no, there's no such option in MX
However, I have another method to make it a bit easier.
Say if you are looking for different E-books, but aren't sure which E-books you already have. Queue up for all the files you are interested in from the search results. When you're done, go to a chatroom and browse yourself. Look through the list, the files you already have will now show up as yellow or blue. Now you have a list of which files you need to remove from your transfers window.
I know this takes some time if you're downloading many files, especially if the file names aren't the same (look at the file size instead) but that's the easiest way I've found