Start with 3 parts paint to 2 parts original Windex and go from there.
The other paints should be about the same.
Did you thin with the water or Windex? Windex is what a lot of people use to thin the craft paint type acrylic paints, like GW, Vallejo, Reaper, etc. I believe the ammonia is supposed to help adhere a little better. But water should work too.
And no the Windex doesn't affect the color of the paint at all. I've used a whole lot of Vallejo Game Color White Primer on my minis thinned with it and there's no blue tint at all.
By the way, if you're using the airbrush to do minis with I would highly recommend Model Master Acryl white or grey primer. I've changed over to that recently. Super smooth.
So long folks!
I have to agree, I use ammonia to take bad acrylic paint jobs off. Iso alcohol is what i use to thin acrylics for spraying but I picked up a bottle of Vallejo airbrush thinner and it seems to work fine, thinning to regular airbrush consistency.
Now, metallics. Oh boy. GW old gold and copper have gone round and round many a time using just a brush and "magic wash" as outlined on the Reapermini.com forums and The Craft page at that website,and I wont consider airbrushing it. I have a hard enough time cleaning it from my brush, I dont want to try the AB. I will use my Alclads for anything metallic, or common Model Master enamels.