changing colours

hey guys,

Im busy going through the wikibook guide,

but I can’t figure how to change the colour of objects.
I finally found how to change the world colour, and there is a button before it which I think is supposed to be for whatever you have selected, but I changed silver to yellow and it didnt change in the preview or the render…

trying to change the bolt to yellow…

>.< plz guys~~~ help me >.<

You have that Material set as a Node. Either click Nodes to use it or create a new material.