Color for Upgrade button should better reflect whether upgrade is possible

Upgrade button is currently a bright, inviting green whether or not you have the materials to actually perform the upgrade. You should be able to get a better sense of whether the upgrade is possible without opening the dialog (which does have a Level Up button with two states, indicating whether the action can/cannot be completed). I shouldn’t have to open a screen that I then have to back out of when I discover I can’t perform the action; I should have some indicator before opening it to save the step.