Being without power for extended periods of time means finding things you can do in poor light. I can spin pretty well in the dark, and I don't usually have to look too hard at my knitting if it isn't something too complicated. Unfortunately the knitting project I was working on when the power went out was these:
The same thing happens in reverse all the time - you see some knitting with colors that you love, then see the yarn it was knitted with, and think "I would never have pictured this yarn coming out like that!"
Spinners experience this all the time. See how bright and almost garish the different colors look in the unspun wool? The colors become much less intense in the finished yarn because of the the blending that occurs during spinning. Because of this blending, it can be hard to see from the yarn that it will create subtle stripes when it's knitted up.
The striping is more prominent in the first example because I used colors with strong contrast. In this second example the colors are much more closely related, both in hue and value. Here, you don't get strong stripes so much as a subtle shading.
Of course, the final effect will always depend on the size of your knitting. Smaller projects like socks will end up with much wider and more prominent stripes. Sweaters and shawls will have narrower stripes - sometimes maybe only one row before the color changes enough to be noticeable! Still, it's always nice to at least have a ballpark idea of what a yarn is going to do before you plan your project.