Masking and Painting a "Foamie"
Paint over the area that you want to mask an inch or so more than you want
with the lightest paint you are using first.
Let this fully dry for a few hours.
Next apply the masking tape. After you have applied the tape, paint with the light colour over it overlapping into the 1 inch area of the light paint. This will seal the tape along the colour line. Let this dry for 1 to 2 hours maximum. Next apply the darker colour over the taped area overlapping the tape thick enough to hide the lighter colour.
Let this dry for about a ½ hour to 1 hour maximum and carefully remove the tape at a very sharp angle. You should have a great straight line between the two colours. Let the darker colour dry and then finish applying the darker colour to the rest of the aircraft.