Leave the button area selected. Call it Color. Click on the Floodfill tool to select it. In the Fill Style choose Solid Color. Leave the rest of the values as is for the defaults.
Flood fill the selected area with the foreground color.
It will completely cover the texture with the green. The opacity or heaviness of individual layers can be adjusted for different effects. Play with the settings until you find something you like. Use PSP, BladePro or some other plugin to apply effects to the button.