Cutting the extended seat mast to size and using tape to try and come up with a three color paint scheme.  Any ideas?

 Just a little pictorial of how I do my miters.  I use the BikeCad Pro software to make the patterns, then cut after determining the position on the tube.

 I finish up the outside edges with a belt sander.

Then get the inners with this very aggressive sanding roll.

Finally, I use a piece of head tube diameter and 80 grit to finish it off.