Great! I highly recommend watching the
tutorial videos on the website if you haven't already done so, and there's no shame in watching them again if you have. I think I pick up something new each time I do! Taking a glance at the first one, I'm reminded that the mini-inspector visible across the top of the diagram (just to the right of the numbers showing the size and position of the selected object) allow you to quickly change fill type, color, line stroke, etc. Of course, with the default color being white, they aren't quite as apparent as they are in my screen shot!