UMG add button, animation
key the alpha channel of the color of the button
without expanding open the key to show r, g, b, a channels in sequencer, right click on the key and look for the properties. it crashes.
ideally you should see the color of the value of the key you selected on. if there's no key at the time for the channels that you manipulate, the color displayed should be right, but it wouldn't be able to set the value for channels that don't have keys. if there are no keys for a channel, it should set the default value of that channel.