Just a graphic set replacing colors for some texts of the game (menu elements, title cards and others). Not really anything special, just makes the game looks weird.
(BTW: An interesting "first impression" was that I was reminded of the two default color sets of those very old CGA graphics cards for old PCs from the 80's (before they were replaced by EGA graphics cards, which were followed by VGA cards) -- that was either "black, white, pink, cyan" or "black, red, yellow, green" if I remember it right... )