I heard that a pink undercoat works well so tried it on an
airfix fiat g50 a few years ago , it was better than grey but produced about the same results as a white primer so i would just use white. Great tip from john there though ,adding a drop of white to the first few coats to increase the opacity - I'll definitely be using that little gem -cheers john!! As a footnote , i dont seem to remember having any problems when i was a nipper ,brush painting humbrol enamels , their matt yellow was opaque and covered everything (mind you no one primed anything then either ,just slap it on!!) so maybe this is a modern acrylic (possibly modern enamel too) problem ? Maybe the Nanny state has made all the paint manufacturers make them all super safe so all the good old hazardous ingredients that used to make the paint actually do its job properly have been removed for our own safety (i dont know about you but ive never been tempted to drink gallons of model paint but thanks Health and Safety guys for assuming im stupid enough to and looking out for me!)