This is a very brief introduction to the origin of color in nanoparticle systems. A link to a video is included in the slides that shows the addition of the reducing agent to the gold precursor solution. The link is also available as a Web Resourse (below).
A student should be able to explain the basic ideas of how color arises from metal nanoparticles.
This 5-slides would be good for a very brief introduction to nanoparticles and color. I use similar presentations before my freshmen students make nanoparticles for the first time.