It was on the colors tab, the one that has also the intent and the setting for reference light and color space. There was a slider labeled color gamut about in the middle and it started at 100%. It could slide up to 200%. I was trying to fix a washed out appearance, and I slid this up to 200%, but I changed several things at once and so I'm not sure what effect this setting alone had. (I know, it's better not to change many things at once, but I was rushing to get a project completed.) It appears that the actual solution to the washed out problem was changing the rendering intent to "perception photo".
The HTML manual that appeared when I clicked for help did not look like the corresponding screen in Turboprint. But I see that the PDF manual you have on the site does look like the screen I see. (I think the main difference was the appearance of the color/gray tone controls.) But the display I got looked just like what you have in the PDF manual except instead of "Saturation" it said "Color gamut".