The color on that turquoise yarn is still vexing me. But I think I've figured out the first step in fixing it, which is correcting the saturation. I was reading about photographing intense reds (related to red yarn, of course, because that's apparently all I take pictures of anymore...) and they mentioned that since the camera has red, green, and blue color channels, if you overwhelm one of them, you can get less-than-ideal results. I think that's part of what's happening with this turquoise.
Here's an SOOC shot of the scarf-in-progress:
Ack! Color overload!
Here's a desaturated version of the same image:
Much better. The color tone is a lot truer, although it's still not completely accurate, and the brightness of the yarn is gone. I think my next try will be to take pictures of the scarf with a lot of other colors in the frame, to hopefully even things out. Cross your fingers!