The colour gamut of your printer is also affected by the paper that you use. If you use very white paper, then brighter colours can be printed as the whiteness of the paper shows through the ink. It the paper is more creamy coloured, then the colours printed will be slightly duller - you certainly will not be able to get a pure white. The paper finish will also have an effect - gloss papers tend to have a larger gamut than matte papers.