Since the color seems to be a lighter color, it usually works.

Medium-to-lighter colors are just fine with doing this.
Deep colors can be REALLY adversely affected!
As you move into darker tint-bases, more TIO2 pigment is left out. This makes these base much more "sheer", so going lighter with a deep color WILL result in a less-than-desireable result!

...UNLESS you like putting on 6 coats....

Faron

Ok, thank you. I think I might have them make me a sample just to be sure. I would hate for it to come out a color I don't like, when I am ok with the 100%.

I'll follow up in case someone else is researching a similar question.

I mixed SW Iceberg 50% and the walls look white. No color at all. I wanted a light grey-blue but worried it would look too blue. The bedroom is dark, little natural light.

The walls look bright silver white. Not bad but not what I was looking for. I would test a wall before mixing 75%.

Jane

Did you try the Iceberg first? Does the paint color you have now look like what the Iceberg did when it was wet?

I guess that is what I am going for...what the Sleepy Blue looks like in the can or before it dries.

I ended up getting a sample of the 75%, just to be sure. It looks nice, what I was going for actually, the wet version. We decided we like the original color better, I'm glad I got the sample. I'll have to remember this trick in the future though, just a subtle difference might help with other colors.