You have two options depending on how many different colors are required for the number of objects. If all objects will be opposites of each other, then you only need to have the fill and stroke colors, in the tool bar on left side you will find the two color swatches at the bottom of the bar. Just to the upper right of them is an arrow. Clicking it will switch between the two colors
Now if you have more than two colors, you will need to save the colors to the swatch panel. You can then click on the color as you need them.
