from memory nick when i had my paint mixed to do same as you the undercoat/primer was a mixture of 90 white and 10% black .
personaly id not touch halfords paint mixes as ive seen some real shockers mate especialy as your going to be colour codeing .
if there small items ie fog surrounds etc etc why not just go to fords and use there pre mixed cans .
done this on mates car for him and colour match was spot on and you can get a decent finish with this kit ie paint and laquer.
Thanks for the reply i have ordered the performance blue paint from ford.
but i dont know what color under coat- primer to use as there differant colors ie
i done a paint test without any primer and it looks to dark so i need to use a primer coat so i am able to get a good color match.