Set transparency to button

[WallaceGromit]

In designer mode it is possible to give a transparency grade to the buttons.
I would like to set total transparency as default, so I see the background picture, and set a slight shade of white once the button has been pressed. How can I do this?

[actech]

In design mode, use the palette

You can set transparency using blocks as follows

[WallaceGromit]

Thank you very much: setting Color to “rgba(255,255,255,0.1)” I got what I wanted.