I was test-snapping around the house with the camera's auto-ISO set to reach iso6400. I have NR set low to retain detail, but the screen view clearly shows some color noise. I changed the custom image setting to Muted, bumped the hi-low key up a bit, and the results are much cleaner - less colorful indeed, but I'll take that compromise. For times when the images really count the raw option is definitely best, but Muted jpegs are a fast answer when fast is important.
I don't doubt others know of this, but it was new to me