Don't wear red on the day of the OSU game, other than that anything is acceptable (obviously no wearing of OSU shirts in general - but this should be common sense). (There are someother red teams I would also recommend never wearing any of their gear: #1 would be StL Cardinals)
As for what to wear to the games - I have always been on the side of wear whatever official gear you want to the game. You pay 80 bucks for a Harbaugh jersey you have the right to wear that even if it is supposed to be a "maize out."
I don't think the maize out is a great idea because 1. things like a black out, Nebraska's sea of red and the penn st white out are easy to do - because everyone has a red, black or white shirt in their closet. Not everyone has a maize shirt, even if your an M fan. And like I said before a lot of people want to wear their expensive jersey to the game, which is perfectly fine.