You mean, if the user has clicked the button…to gray it out/change the image? You could use variables….once the user clicks the button, change the variable. Depending on what the variable is, you can show the “unclicked” image or the “clicked” image. Basically, hide the “Clicked” Image, make it appear on top of the old button, and show it when the variable is activated.
Or, you could simply add an action for “On Mouse Click” “Show” and choose the “clicked” button …..and change the button that way.
I’m not sure if your button is a true button, or simply an image that you use as a button (by placing an action on the image)….sorry for my phrasing above. I noticed that I jumped between “image” and “button”! 🙂