This is an update on what I mentioned last time on undertones. Preeti of Rambling Roses asked a question about using fabrics of the same color with different undertones in a single color quilt. I wrote her back, and my email got a little long-winded, but I realized that the way she had phrased her question helped me realize I hadn't clarified things thoroughly and it gave me a different way to think about it.
I referred her to my blog post about my churn dash mini quilt.
I used a variety of blues, but they're pretty similar in undertones. The only exception is the Cotton and Steel "Dottie" print in the corner which is warmer and has just a hint of yellow. I went ahead and used it because the dots are white. Here are a few of the navy blues I used, along with a couple new ones, and if you look closely, you'll see they're all a little different. The herringbone on top is the darkest and is almost black, while the Michael Miller Stitch Squares is almost a little purple. But they're all really within the same range and use the same undertones, and I think they work well. A little variation is interesting.
The white in the design is a great hint at the undertone. If a print has white in the design (as opposed to cream or ivory), it will most likely have a "clean" undertone. I personally wouldn't put prints that used cream with prints that use stark white. But that doesn't mean cream is bad, of course. It all depends on what you're after.
These two pinks have different undertones and I know it's very, very subtle. I picked these ones on purpose. The pink is almost identical, really. But the Cluck Cluck Sew floral on the bottom has a white design while the dots one on top has ivory in it. I bought it to use with my daughters' quilts, not realizing at the store that it wasn't white, but in the end, I couldn't because the undertone was wrong. It looks a little dirtier next to prints that have a nice, clean white undertone.
This isn't a hard and fast rule--if you like something, you should go for it!