In the image below I want to make the head a different color from the body. Is there a way I can connect the two red points so that the head is a separate shape? If not, what's the best way to proceed?
I draw a character in "one piece" then I break it up later as I need to.
First draw a line to connect those two points at the neck. I would reccomend that you have an "extra point" in that line. This is helpful later if you need to adjust how the shapes interact especially if you have a stroke. I also find that getting shapes to create properly in some situations only having two points on one side has "issues". Moho always "closes" the shape. Sometimes I don't want that... so by adding the extra point on that cross section I have more control.
I also like to have extra points so that if one shape "overlaps" another shape I can use those points to control the visibility of the strokes. If two shapes are "connected" like an arm... the stroke is covered on the joint area by the unstroked edge. I move those extra points so that doesn't happen.
Next use the Create Shape Tool and select the head shape. Hit the space bar.
You now have a new shape for the head... you also have a shape for the head AND the body "underneath"... you could delete that shape and recreate a new one just for the body by selecting only the body shape... that is up to you.
If you have a stroke on the shapes and don't want a line at the neck use the Hide Edge tool and click on those lines you don't want stroked.
I usually make the arms and legs two or three shapes each (bicep, forearm, hand)... this way if the arm bends over itself it doesn't create those "holes" that happen when a shape overlaps itself.