Sketchup will only draw flat geometry in ‘blue’ orientation. And if I draw it in ‘blue’ orientation, it won’t allow me to rotate it thru 90 degrees into the green orientation – the protractor sticks stubbornly to blue.
WTF?
Yes, I know I can draw a cube and then Sketchup will graciously offer me a rotate protractor on any of its faces, but that doesn’t help me get where I’m going.
It all depends on where your mouse cursor is and where it’s facing. SketchUp will try to guess what plane you want to work on. Try orbiting your view around so that you’re looking more straight on the plane you want.