You can use Winzip - worked for me

HCL Notes/Domino 8.5 Forum (includes Notes Traveler)

Subject:

I made my unread "red" by opening and extracting with folders intact the contents of the jar file that contains notes.css. Then I just used notepad to edit black to red (lowercase is important when designating the color). Then I packed it all up again preserving the folder structure as a zip. I simply renamed the new zip file to jar with the same name as the original and put it back.
Finally, before starting Notes I deleted platform.xml (found below (data\workspace\....)which is a file that caches the contents of the last notes.css read. This forces a new read of the notes.css file. Everything has been working flawless for several days.

Feedback response number WEBB7JAULB created by ~Gus Chukikonyoni on 09/08/2008