How many coats

EdGrune

The pigments for red & yellow paints are generally thinner (acrylic and enamel) and may be more problematic in achieving one-coat coverage.

Also white and orange - moreso with gloss paints than flats. At least this is my experience with Tamiya acrylics. With Tamiya acrylics, flat white, yellow and red have a good pigment density.

YMMV with other brands. 

Foxy

Ok this is probably going to be the noobest question you've all heard in a while but here goes... 

How many coats of colour(the same colour) do you guys put on your model parts?... Is there any hard and fast rule to this? Or just personal preference?

I've primed my pieces and airbrushed a coat of colour.. And in all fairness its well covered.. Just wondered if one coat is enough or if there's a valid  reason to apply a second coat before clear coat?.. its acrylic paint for information purposes 

 

The pigments for red & yellow paints are generally thinner (acrylic and enamel) and may be more problematic  in achieving one-coat coverage.  Green & blues are better.  
Go slow, multiple light coats to achieve coverage instead of one heavy

My sister once told me the secret to cooking scrambled eggs is to plate them before you think they are done.

Works great every time. I'm trying to learn to apply this to my airbrushing because I'm too heavy-handed and never know when to stop. I agree with Goldhammer and Tojo, with airbrushing, less probably is better.

Yes just enough for coverage or whatever effect you are trying for the last thing you need is thick coats of paint obscuring fine details

Since I don't do any pre shading, I just spray enough coats to get full coverage.

If preshading you might have one light coat in some areas and more in others, up to and including full coverage.

All depends on the effect you are looking for.