Almost all aluminum spars are anodized in order to slow down corrosion. Almost all boats have aluminum masts, hence - you will prbably end up with an anodized mast on your boat.
Anodizing can be done in colours, but it is usually just silver on boats. You will sometimes see painted masts, (usually done by owners who have been watching a lot of Martha Stewart reruns
), or gold or black anodizing.
It is preferable that your mast be anodized if it is aluminum.