Thanks Funcolors - you've supplied good advice. It was along the lines of what I was afraid of - I'm not sure what I would be asking for at the paint store and I don't think that this particular store is well-versed in paint colors.

Hm, so where does this leave me? I could try a sample size with half the colorant or search for another color that would work. The stairwell gets a fair amount of light and I want a small amount of color to contrast with the skirt boards but not be overwhelming and still go with the adjoining Pitt Buff.

Anyone with ideas?

Thanks a bunch.

How about going with the next lightest color on the paint strip?

Funcolors gave you the professional knowledge-based answer.
Here is my DIY-er response.
I tried mixing a stock color (SW 7621 Silvermist) at 25% for use on a ceiling just last week. It was the first time I've tried such a thing, and I'll never do it again. What I ended up with can only be described as "IT'S A BOY" blue-
fortunately I'm only out a quart of paint and it wasn't a big job.
I think that certain color pallettes, BM Historic and SW Concepts in Color among them, are harder to work with than pallettes with the traditional "6 to a strip" colors. I've always had great success with using colors within a strip for adjacent rooms or wall/ceiling combos, and in the future that's what I'll stick to.

Well, gotta try it at least once to know if it's for you or not.

Some colors reduce/increase more gracefully than others. That's advice the professional paint store staff should be providing as well -- they should be able to tell you if cutting a formula is a good idea or not. Finding the right expertise and paint store is really important -- and it's not always easy to find paint people who are color competent too.

I know many people like to take the wall color and 'cut it' for the ceiling. One version of the "right way" to do that is 10 parts white to 1 part wall color. Of course, which "white" matters. Ben Moore's "White" or "Super White" are two good contenders for this job.

You can do 10 parts to 1 part in a small quantity first to see what it looks like. You already have the wall color so you can buy a sample pot or a quart of white to mix a tester of custom ceiling color -- this is an inexpensive way to try your hand at cutting color if you're itchin' to give it a go.

If you like the color you get, you can do the math and mix the total quantity you will need for the whole ceiling. Don't forget to mix extra to save for touch-ups.

I don't mix my own colors, but I usually buy paint at a smaller paint store, and the guys there (Par Paints in LA), have always done a good job for me--I've had F & B London Stone mixed at 1/2 in a Ben Moore base, and I was pleased. But I wouldn't trust a big box store to do this right, which may be my own prejudice.

I had read someone here say they painted their ceiling at 1/4 the strength and I wanted to try that in my bedroom. I asked the guy at the paint store and he looked at me real funny and said he needed something to color match. After an awkward conversation about it, finally we decided to have him put the quart recipe into a gallon can. Anyway, it worked out perfect. When I started painting it looked terribly green against the unpainted white, but by the time I was done it looked like white and was a nice transition from the walls.

rdquilter - I like that idea. Makes me think that maybe I could have them put two quart recipes in a gallon to get to half-strength for the stairwell.

I don't really want to try mixing on my own. I'd be worried about getting the color consistent from one gallon to the next.

Thanks to all for the good advice.

Has anyone mixed BM Quiet Moments at half strength or 75 %?

try three tablespoons of quiet moments with one tablespoon of stark white and see if you like the result. That is such a subtle color that it will probably work out fine.