Yes, you will be able to set your line color exactly as you want. Also all the coloring will come as mentioned above. Straight lines and circles are “controversial” because I want to keep everything straight forward and as “analogue”/nonetechnical in feel. Of course it can be highly technical and complicated under the hood. But we are contemplating doing lines and circles in an easy and user-friendly way. We’ll see how it goes. 🙂
By the way, you can actually change your white transparent background to black (or gray) in the current alpha. Try to see if that works for you and let me know: Paint -> Transparency Shown As -> Black.