Plymouth is the name of the subsystem that takes care of the startup process in Ubuntu. It’s supposed to be a purple (auberdine actually) screen with a nice Ubuntu logo and an activity indicator. But it can degrade to be simple white text on a purple background.
If you are seeing the yucky looking text, then you, like me and many others, are using proprietary video drivers. I suggest you head over to Kyle Baker’s blog for a handy script that fixes it for you. It seems odd to me that such a big cosmetic issue has slipped by Ubuntu QA for two releases now.