A few years ago we were selling our house so I re-painted the entire thing. Since it was going to be sold and I just wanted to freshen it up I went the cheap route and color matched a Benjamin Moore colour using Behr (at Home Depot).
What a disaster! The computers used for colour matching can never get the same formula unless you get all cans at the same time. You will be in big trouble if you run out of paint and have to get another can. Even using the formula from the first purchase the remaining can was way off. After repeated attempts to match to the original/color matched order, and multiple (mis-matched) test spots on walls (argh!) it became clear I'd made a huge mistake trying to copy a paint colour.
A Home Depot paint manager gave me the low down on why it just doesn't work when you copy a paint colour:
After a product (ex. latex flat emulsion base white) goes on the big box shelf the paint manufacturers update the product on an ongoing basis. Therefore you can get a can with an 'older' (last months) formula and a can of the 'new' formula. The cans will look exactly alike; the manufacturers have simply 'tweaked' the base formula which will alter the colour outcome.
Each manufacturer has their own 'white' base to which colour is added. So when you take a Benjamin Moore, Restoration Hardware, C2 etc. sample in to colour match you will never get the same...because they are formulated using a different white base.
The colour matching done at the big boxes only uses the computer to create a formula. At least at specialty paint stores when they colour match they will take the computers 'match' and then, by eye, tweak till they feel it is right. This can take a whole day of them playing around, a few hours or few minutes.
Here is what happened when I tried to touch up some spots with a different can of paint purchased at the same time as the original wall colour:
I went back 3 times trying to get the colour fixed...many many cans later I actually spoke with a paint manager. I got my money back for the original paints which was very kind of him.
I will never again colour match at a big box.
I wish I could say I'll never colour match again but C2 is to damn far away and Farrow & Ball is too.
I'm very fortunate to find a specialty paint store where the paint technicians take their time and will not release the paint till it is a match.
The point to all this rambling: I ultimately used Benjamin Moore's Aura paint. Despite the cost of a gallon of Aura you actually use much less than you would of the big box paints.
1 coat with Aura (like C2)
New drywall or patched? Just paint it one coat with Aura and you are done.
I had already done 2 coats everywhere with the 'color matched' paint...then the touch up fiasco and then repainting in Aura.
Thankfully I only had to do 1 coat and no priming any patches.
Now that is a lot of time to relax and enjoy the job!