Sometimes when using Adobe Illustrator I need to get a range of tints from a certain color, so I'll drop the opacity to, say, 75%, 50%, and 25% on a white background to get there. It's the quickest way to get what I want in that moment, but then it comes back to bite me later when I put something underneath and then I have visibly overlapping layers.
What I want to be able to do is get the value of the color that I'm seeing. In Photoshop I'd do this by putting a white layer underneath, merging the two layers, and then sampling the color. Is there some sort of trick I can pull in Illustrator to do the same thing?
If not, is there a different (and preferably simple) way to add white to a color? Changing S and B values in the color picker is the only thing I could think of in that regard and isn't always terribly simple to do...

