Request for guidance on sources to help me figure out how to do simple thing
What you want is a three position two pole rotary switch:

It's circuit is like this:



The three positions are 

position 1: contacts 1 &amp; 4 selected -- used for Blue (contact 1) and White (contact 4)
position 2: contacts 2 &amp; 5 selected -- no contacts used (off position)
position 3: contacts 3 &amp; 6 selected -- used for Blue only (contact 3)


Connect Blue to terminal 1 and 3, and White to terminal 4.  Leave terminals 2 and 5 disconnected for the center off position.  Also leave terminal 6 disconnected.
Connect your drive voltage for Blue to terminal C1, and White to C2.

One such switch is the ALPS SRBM131300, available from Mouser for $5.75.