They have just discovered plasmons I think. It has been known since the 1930's that the transmission of visible light and its colour is due to small spherical grains of gold in thin films less than 100nm. Thin films are made of these discrete grains as they grow from the first atoms to 'stick' to the substrate. The red colour in red glass comes from gold particles in the glass.
You are correct sjastro they should better specify what wavelength etc is involved.
A cursory search revealed this old gem
http://www.jstor.org/pss/95606
Bert