Yellow is a warm color along with red and orange.  It is associated with the solar plexus and the third chakra which is located there.
This energy center is associated with self-esteem and ego.  In more spiritual aspects, it is the chakra that links us to the spiritual sun and, since everyone is linked to the spiritual sun, we are linked to everyone through it.  As small children, we always painted pictures with a bright yellow sun in the sky, even though the sun is really white.
    In color psychology, yellow is considered a cheery color, but can also invoke feelings of frustration and anger.  An interesting aspect of this is that sitting in a room painted or decorated in yellow can increase metabolism.  Some find yellow energizing.  A bouquet of yellow flowers is usually considered cheerful and sunny.  Yellow helps to have a clear mind, confidence, strength and balance.
    Not everyone likes yellow though.  It has been associated with some negative things such as cowardice.

Yellow in legends and folklore:

From the Cherokee legend "The Song of Cherokee Rose"
"I took a lovely vine with the roots that grew on my old home. It has a beautiful, small white flower with a little yellow sun in the middle that smells sweetly. This lovely flower with its sweet scent will remind me of my home and my father and mother."

And in the great yellow-jacket legend, a giant insect (yellow-jacket) as large as a house would carry away animals and children.

A legend from WW2 says that when the Nazis ordered Jews in Denmark to wear a yellow star so they could be easily identified, King Christian X of Denmark said all Danes were equal and he, and most other Danes put on the yellow star armband as well.  Historians say this legend is not true, though the Danes did do much to resist the Nazis.  Instead, most Danish Jews simply ignored the order to wear the star.

If yellow is one of your weaker colors, you can strengthen this center by wearing yellow clothes and gems and gold jewelry, eating yellow food, and getting sunlight.