Most of the time large telescopes are collecting light for a spectrograph, which spreads the light out into a rainbow. Each kind of atom or ion has certain special wavelengths which it can absorb or emit. Atoms in the cool outer layers of a star absorb light coming from the hotter regions within, producing dark absorption lines across the spectrum. These can be used to identify the atoms that make up a star. To see the lines produced by any element, use this Java applet .
Color film does a very poor job of representing the continuous range of colors in a spectrum.
It takes a lot of work to make a decent printout or display of a spectrum. While a picture may be worth a thousand words, a graph showing brightness vs. wavelength has much more quantitative information than a picture of the spectrum. In the figure this graph is aligned just below the picture of the spectrum.