I agree that it doesn't really matter what colour primer you use, although I always use white now. As Allen suggests, though, white can be better under some colours, but it can depend on how thick your layer of paint is.
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Also, if you're preshading, then it really won't make any difference what colour your primer is.
Unless of course you are using my pre-shading method then white is a must
To pre-shade or not to pre-shade To pre-shade or not to pre-shade-part deux A tip with Halfords primer, when it is dry it can be slightly rough (usually?) I "polish" it using 0000 grade wire wool. This creates a lot of dust but really smoothes out the primer, a must for a good finish. The reason for using wire wool (0000 grade is very fine) is because it acts like emery paper but doesn't sand off detail. After "polishing" the primer make sure that you remove all the residue, blow it off, wash it off but get rid of it. Before painting I use a "tac rag" or possibly some low tack tape, to go over the surface to pic up any bits.
Another tip for a good gloss finish is to build it up gradually. The first thing that I would do is apply a mist coat. This is basically what it says, hold the airbrush off the model by 300mm or more and spray with a widish pattern. You are not trying to cover anything but are looking for the paint to form tiny droplets, evenly, all over the model. This will form a "key" and stop the finishing coats from pulling away from edges and panel lines of the model. This is a trick employed by car modellers, to help them get that "showroom shine". The next coat is applied straight away, Get in closer, 100-150mm, turn down the width of the spray pattern and with the paint at the same consistency as for the mist coat (about 50-50 [thinner to paint] but it depends on the paint) spray in overlapping bands but
do not try and cover the complete model. This first coat should be thin. There are now several schools of thought on the best way to proceed. One would leave the paint to dry, sand out any impurities, dust etc. remove the sanding residue, as before, then apply another similar coat, painting the bands at 90 degrees to the first layer. Repeat again, but this time thin the paint a little more, I.E. 2 more layers at 90 degrees, waiting for the paint to dry and sanding out any impurities between each. After sanding out the last coat apply the final coat, again thinned more. When dry sand again, if necessary. The sanding should be done with very fine emery paper, after the final coat the surface is sanded, lightly, all over then polished, using plastic polish, but tooth paste can be used.
The other method is similar but instead of waiting for the paint to dry, wait 15-20 minutes, then pick out any impurities with a fine pointed pair of tweezers, then apply the next coat. This second method is one that I have done and it worked quite well. If I was after a gloss finish now, I would probably have a go at the first method, but this is more for cars than aircraft. It was also based on using enamel paints and I don't know if you can get the same results if using Acrylics.
For an aircraft model I would be tempted to paint it in a satin finish rather than high gloss. It does depend on the scale, satin for 1/72 and 1/48, gloss, possibly, for 1/32 and probably for 1/24. The choice is yours of course. Also for aircraft I would alter the final finish by using varnish, matt, satin or gloss.
This might be similar for cars but I don't build cars
Having said all that I actually paint aircraft models differently anyway, as I'm not after a high gloss finish
Mal