When it comes to colors, the number of options open to you will greatly depend on the material that you select for your shower base or pan. Although each one does offer some scope for personalization.
Whichever color you choose, you're going to want it to match the aesthetics of your bathroom. A good way of doing this is to coordinate the base or pan with your wall tile or color. You don't necessarily need it to be the exact same color, but it's good to work with shades of the same hue.
Avoid mixing and matching warm and cool colors. If your bathroom is warm, good colors to go for are shades of bronze, biscuit, or almond, and if your bathroom is cool, grey, silver, and nickel will work best.
White is, of course, the most common choice - this looks naturally elegant and will complement most bathrooms. Choosing a white base or pan also makes things easier when you are looking to redecorate the room - it won't limit your options.
Black is another possibility here, but this really works best in more modern feeling chromatic bathrooms.