Images below are all unmodified 100% crops from the the Sony Cybershot DSC-H9. ISO was set on the camera but exposure was set to aperture-priority and white-balance was kept on automatic.

Here the H9's automatic white-balance system shows how inconsistent it can be. Although, each shot below was taken eight times. The white-balance changed dramatically between consecutive shots. The ISO 400 and ISO 800 shots in particular never had the correct white-balance.

Long exposures such as these ones stress digital camera sensors more than any other type of photography. While ISO 100 is fairly clean, ISO 200 already shows elevated noise levels. Starting at ISO 400, noise is apparent even in small prints. Forget about using ISO 1600 and 3200 for long exposures. For that, a DSLR like the Pentax K100D or the Canon Rebel XTi is recommended instead. See the DSLR Guide model page for more options.