"Decor" paints are the deep rich colours that are often used for decorative trims or accent walls. But home painters are constantly complaining to me that they can't get the right colour at home, or that it requires three and four coats to cover the old wall.
To understand what is wrong and how to get these paints to work, you need to think a minute about how you get a deep rich colour in a paint in the first place.
Most paint starts as a white paint and then you add colorants to it. Imagine how much colorant you would have to add to get the white to come out dark and rich. By the time you had added enough bright red colorant to a white paint to have a bright red colour, not pink, you wouldn't have much paint mixed with all that expensive colorant. So the deep rich colors are only possible if you use what is called a "neutral base" paint to start with.
But it's the white pigment in regular paints that gives them their hiding power -- with a neutral base, any colour or colours already on the wall will show through.
On this TV segment we showed this with a richly coloured transparent acetate. When I put my hand behind the acetate, you could still see my hand. It would take many layers of this acetate to hide my hand. If I put a green wall behind it, the colour you would see would be a mixture of green and red, not the red you were looking for.
So to get decor paints to work, you need to first put a primer on the wall to cover any other colour that was already there. And to help get the rich colour you are looking for with fewer coats of decor paint, you should have the paint store tint your primer "in the direction" of your final colour. The paint clerk will understand what "in the direction" means in terms of colours. Basically it means something lighter than but compatible with the final Decor colour.
The primer will be much lighter than your final colour because of the white hiding pigment in the primer. But you won't get white or some conflicting colour showing through the top coat of the slightly transparent Decor paint.
A primer is necessary to get the decor colour you saw in the store on your wall at home and a tinted primer reduces the number of Decor coats you will need to apply.
I would like to thank the Pratt & Lambert paint company for explaining all of this to me and for setting up the acetate demonstrations board to help explain it to you on the TV show.