Based on what you've mentioned here's the situation on the three wires on the switch as I see it. One wire(red or black) is a hot wire on the line side of the switch, a second wire(red or black is a hot wire on the load side of the switch and goes to the fixture. The third wire(blue) may be an additional hot wire on the load side of the switch to control another light/fan/fixture form the switch. What you haven't mentioned is the neutral wire on the light fixture, you must identify this wire and connect it to the white wire from the wall.
It would make it easy if you have access to a voltmeter. With the switch off connect the black wire from the wall to the black wire to the switch. The voltage on the other two wires should be zero if black is the hot wire on the line side of the switch. Turn the switch on and there should be a voltage on the red wire and possibly blue wire. You may have to swap the red and black wire with the black wire from the wall if the test proves wrong. I'm assuming you don't remember how it was initially wired or how the blue wire was connected.
I'm making a lot of assumptions here but if you properly test each wire as you go and identify the neutral wire for the light you should be OK. The blue wire is probably not used in this application. Good Luck.
ON EDIT: There should be a way to ground the light fixture. The ground wire is different than the neutral and is either green or bare and is connected somewhere on the metal part of the light fixture.
2007 Newmar DSDP 4023
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