The comparison the narrator makes between her memories and "a fresh watercolor painting left out in the rain" is a simile that aims to convey that her memory of "those" days isn't totally clear, they intertwined with each other and may slide, vanish or dissolve like a fresh watercolor painting. However, the narrator began the sentence saying "For the most part", meaning that not all their memories are unclear and there are things they can recall. In conclusion, b) She is not sure if she remembers the exact details of everything that happened, but she can recall the way that she felt when she was growing up.