You just need a simple switch called a 'Single Pole Double Throw' (SPDT)
This kind of switch has three terminals. Attach the one in the center to your indiglo power wire; one side to the +12V; and the other side to the parking lights.
When the switch is in one position, the indiglos will be attached to the +12V; with the switch in the other position, the indiglos will be attached to the parking lights.
Make sure that there is a fuse somewhere between the +12V and the indiglos though! There should be some kind of always-on accessory fuse already in your under-dash fuse box. Take the +12V wire from there.
Simple.
Here's a picture of a SPDT switch - notice the three terminals - this one would work but would be WAY overkill
You could find a nice sized toggle or rocker switch at your local radio-shack.
