Using the shape tools, you can add a color to them any time in the future, assuming the following, you leave the layer as a shape layer, you save the document in a format that supports shapes and layers, like psd or tiff.
Each shape is normally placed on its own layer where you can use the combine options in the top tool bar to set its Boolean state. The states are add, subtract, intersect, and merge.
There is actually quite a bit of information in the photoshop manual about shapes, shapes layers, vector masks, and other vector tools. also read up on layers, layer styles and layer masks as well, these will be important later on. Of the three layers would be useful for your project.