Finding the perfect match paint can be a right pain. These are the best matches found so far:

Red - Plastikote Spray Bright Red

Green - Humbrol Enamel Satin 131

Black - Plastikote Spray Black

Yellow - Plastikote Spray Buttercup Yellow

Blue - Plastikote Spray Harbour Blue

Yellow - Humbrol Spray Yellow

Orange - Games Workshop Fiery Orange

Blue - Games Workshop Ultra Marines Blue.

Gray - Humbrol Enamel Satin 166
Still hunting for a decent SAS Gray and Red Shadow Gray.
Humbrol Enamel does NOT mix with Plastikote undercoat or lacquer!!