Add Alpha Channel to Colors

[JBHoren]

Reference my earlier request #579

Opacity settings (in compton and picom config files) using wintypes (for "dock", the xprop window type for JWM trays) work too well -- the entire tray "disappears". The JWM "opacity" settings in TrayStyle don't work.

One possible solution might be to add an alpha channel to colors (in my case, to Background), and instead of <Background>#656565</Background> I could use <Background>#65656500</Background>, where the 7th and 8th numbers determine opacity.

Would this be doable? If so, might you consider implementing it?