As its sound might suggest, roseate has to do with "rosy." Anything that's roseate is rose colored or pinkish. It's often used in the term "roseate glow," typically to describe a sunset.
Ever heard of the phrase "seeing life through rose tinted glasses," meaning seeing life way too optimistically and unrealistically? Well, roseate can have that sense as well. If you're painting "too roseate" a picture of what college is like to your parents, you're either deliberately or unintentionally giving them a picture that's a bit too good to be true.