There are 3 that I know of. Silver, Black, and the regular goldish color
References :
been playing alto sax for 10 years

Technically, a saxophone could be any color by applying colored lacquer, but this usually isn't done because it sticks out in a group and sometimes affects playing quality. Here's an example of one. http://usahorn.com/tenor/used/LA.Sax.6011841_sm.jpg It's a tenor but the same brand makes altos. Also I just found this, although it's a hand done job, not manufactured by companies (http://www.breakfastroom.co.uk/simpleforum_files/attachments/Pink%20Sax.jpg)

Using a clear lacquer, 3 general colors. Most saxophones you see are made out of brass alloys and will be the standard gold color. Some horns are silver plated and will obviously be silver (http://www.wwbw.com/Yanagisawa-Model-A-9933-Silver-Series-Alto-Sax-460578-i1142610.wwbw) Finally, some saxophones are nickel silver plated, giving it a black color (http://www.wwbw.com/Keilwerth-Shadow-Alto-Saxophone-463380-i1144410.wwbw)

If the horns above have a clear lacquer, they will be shiny. However, manufacturers have begun making horns without lacquer as some people find it has a better sound. Unlacquered horns will have a non shiny, plain kind of look (http://www.sax.co.uk/pmauriat_pmxt66rUL.htm)

Hope this helped and good luck
References :

Lets See:
Blue
Silver
Black
Red
Gold
Green
References :
Playing and seeing them