Drawing onGUI Stuff over each other?

hi there :) So.. i need to create an editor for my Textur Offset, border and slicing. I'm talking about UnityEditor, not ingame. My idea is: Put the Texture in a Box and draw dotted lines, colored fields..etc above it.. But it's not working, since the lines, boxes and Co are drawn below the texture, instead of overlapping it. So the Question is: How can i get GUI Elements overlapping specific GUI Elements? :) thanks for reading.