public static Icon makeTransparent(Icon icon, float alpha) {
		BufferedImage newImage = new BufferedImage(icon.getIconWidth(), icon.getIconHeight(),
			BufferedImage.TYPE_INT_ARGB);
		Graphics2D g = newImage.createGraphics();
		g.setComposite(AlphaComposite.getInstance(AlphaComposite.SRC_OVER, alpha));
		icon.paintIcon(null, g, 0, 0);
		g.dispose();

		return new ImageIcon(newImage);
	}
Make the specified icon semi-transparent using the specified transparency alpha

@param icon the icon to make semi-transparent
@param alpha the alpha value to use in making the icon transparent 
@return a new icon, based on the original, made semi-transparent
Ghidra/Framework/Gui/src/main/java/generic/util/image/ImageUtils.java