Yellow is sunshine. It is a warm color that, like red, has conflicting symbolism. On the one hand it denotes happiness and joy but on the other hand yellow is the color of cowardice and deceit.
Yellow is one of the warm colors. Because of the high visibility of bright yellow, it is often used for hazard signs and some emergency vehicles. Yellow is cheerful.

i thought she would either wear: white, yellow, blue or pink.

My other guesses were red or orange

But it was obvious she'd wear a hat :P She always does :D