When making glamour composites, I often mask out the original studio background and replace it with a background of another color. As an example, here is an original image of my friend Charissa, shot against a chroma key green background:
Once the old background has been masked, there are two ways to add a new solid color background. The first is to add a new blank layer, then double-click on the Foreground Color icon at the bottom of the Tool Bar to choose the new color. This brings up the Color Picker:
Here is what you see when you are choosing a new Foreground Color:
In other words, you cannot see the new color until to you manually use the new Foreground Color to fill into the new blank layer by pressing Option-Delete (PC: Alt-Backspace).
The better way of working is to add a Solid Color layer. You can either click on the "Create new fill or adjustment layer" icon at the bottom of the Layers Panel and choose Solid Color..., or you can go to Layer -> New Fill Layer -> Solid Color... to get this:
What you see while this dialog box is active is this:
In other words, when choosing a new color, using the Solid Color layer gives you a live view of what the new color will look like behind the model. This is a much more elegant way of adding a new color than the first method.