Personally, I would not use white. Here are some suggestions from Ben Moore, which you could have color matched at HD. Here is a link that might be useful: Color suggestions.

The Pottery Barn and Restoration Hardware fell in love with BM paint and thus, they will swear there is no better, regardless. Remember there are a lot more of them out there than there are people who chose to stay with traditional furnishings. I have had no issues with Behr. I have only had a couple issues with SW and BM and that is they never seem to be able to get the color right the first time. I love Pratt Lambert the best. I get the color I wanted. I get the quality I wanted. It is easier for me to shop with the BM people due to proximity but over the years, (since I like to paint at least every 2 years), I have used a lot of paint. Some great paint for me has also been the Olympic/Olympia (whatever it is that Lowe's sells). Having said all that, we covered our gold public area of Cracker Bitz (Lowe's) with one coat of Behr's (Toasted Wheat). Sometimes I think it is related to where you buy the paint, just like the former poster who was not pleased with Ellen Kennon paints. I rarely if ever have a paint that does not go on well, because we clean the walls and mostly prime them (but in the case of the Behr, we did not prime since colors were so close), and I might be disappointed in the colors but I have pretty good results with paint. Back to the priming story. We had an area by our toilet that had to be primed and sanded five times. Painters could not imagine why because they could not see any reason. Later I learned from the tile guys that some problem had occurred with some of the demolition crew taking out my toilet and they had gotten motor oil on the wall which they "thought" they had cleaned. Yes, it was not showing so they "thought" they had cleaned it but the grease was not absorbing the paint and it cost me about $100 extra for that small area because of their "thoughts" on the situation.

The color deck is really nice. It has all the colors on there. I primed in the play room but didn't prime in my craft room & it pretty much looked the same. I was on the paint forum & they said to always prime. My Dad said I didn't need to prime. So I did it both ways. The play room had some puddied areas & were looking rough so after the priming & 2 coats, the walls looked great. I probably wouldn't have had to do 2 coats but I wanted to see the difference in rooms w/ being done the right way & being done a shorter way. I'm not sure of the paint that I painted over as it was done by the previous owners. I'm not experienced with painting so I can't tell you about comparisons to other brands. I can say the smell was minimal, covered well, but I didn't like the egg shell. It comes in semi gloss or egg shell & the egg shell was really dull. The semi gloss just perfect. I would put pictures on here but I don't know how. If you tell me how I would gladly add the photos. If you can't get the color deck, let me know & I will mail you mine as I'm finished with it. YEAH!

As a former paint associate, the likely answer is no for a few reasons. #1 the color you have and the color you need may not be the same base, i.e. you can’t make a color in medium base from light base paint and vice versa. #2 darker colors take more pigment, and sinc the paint is already tinted, there may not be enough room in the can for more pigment and to mix it properly. #3 even though it’s Behr it’s old paint and the store cannot guarantee it was stored properly, so they wouldn’t be able to guarantee the outcome. If they messed up your paint they’d be on the hook for replacements. Having said all that, you might find an adventurous and experienced associate on a slow night who would be willing to try. But I wouldn’t try it during the busy weekend. Your best bet is to see if they have the color in the computer, get a sample and try adding black or whatever is needed to get the desired color before mixing the gallons. If it only needed a little black, you could add the color yourself and just bring the gallons in to be shaken. They’ll reshake anyone’s paint as long as the lid closes tight.