Steven: Long week, huh?
Sharon: Yeah, I'm exhausted.
Steven: Are you doing anything special this weekend?
Sharon: Nope. I'm just gonna keep it mellow, maybe rent a movie and order pizza. If possible, I think I'm going to avoid leaving my house until Monday.
Steven: That sounds great! I wish I could relax, but I'm taking the kids to Disneyland.
Sharon: Well that sound fun.
Steven: I'd rather be relaxing like you.
Meaning: While "mellow" can describe a taste (for example, a mellow dish would be pleasant and mild, not spicy or strong in any way), it can also be used to describe an atmosphere or attitude. A person or place that is mellow is relaxed and laid-back. When Sharon says she is going to keep her weekend "mellow," she means she is just planning on relaxing.
Grace: What do you think of the new math instructor?
Todd: I like her so much more.
Steven: Me too! She's such much more mellow than Mr. Sanchez was!
Meaning: In this instance, Steven says that the new instructor is more mellow than Mr. Sanchez, meaning the new teacher is more relaxed than their former teacher, who was nervous and anxious according to Sharon.