You would also need to project the origin planes, axis, center point (just like other features) to the sketch to allow the sketch to be constrained to them. Once a sketch is fully constrained it will go black (not a requirement though)
I try to plan ahead a little on how I am going to be putting stuff together, and often will use the YZ axis as a mid-plane and center my work around the axis.....but everyone works differently, and your technique will change as your experience level changes. I'll go back to a part I modeled 3 years ago, and ask myself "what were you doing when you made this part?"