Are you allowed to hang curtains? Drapes, throw pillows, art and stuff you love can make your house feel more like you even if you're stuck with plain white or tan walls. A rug can bring in color too. Hope that helps!
I hear ya! We are not even allowed to hang pictures (I have a few, not going to lie). I have some cute vinyl wall art that helps the walls feel not so bare. I agree with Lisa too about the throw pillows or flashy accessories. The thing that has helped me the most is it pick things a little more "wild" then I would normally pick, they add that extra splash. I swear by the 3M hooks that peel off easily too. This may seem silly, but also google "dorm room products"-you can find a ton of great ideas that won't leave a mark and are budget friendly. Good luck!