I’m currently outlining a novel with multiple plot threads. It would be nice if I could quickly change the color of the index card paper just by right-clicking it and being presented with maybe nine choices of color. That way I could easily track each story thread as it appears on the plot’s time line. I’m new to Scrivener and I know the card color can be changed but it doesn’t seem to be as easy and intuitive as it could be.
I’m not sure what more can be done here. 
It already works exactly like you describe. You establish your story threads in the Project/Meta-Data Settings... panel, have View/Use Label Color In/Index Cards turned on, and you’re ready to go. Now just select the card(s) you wish to change, right click on them, and change their colour in the Label menu (or if you changed the name to “Threads” or “Plots”, it’ll print that in the contextual menu instead).
Thanks, Amber V. I’ll try what you described. It still looks, though, like there are too many mouse clicks needed to perform the operation. I want to just hover over an index card, right “select paper color”, and a palette will pop out. I can then select the color I want, and the color of the entire index card will change to that. It should be that quick and easy. Is “label color” the same thing as the color of the index card?
It’s only two clicks if you use the contextual menu, one click if you use the Inspector.
Well, technically speaking, no. The label is a two-part meta-data assignment consisting of (a) a readable phrase such as “Plot A”, and (b) a colour. The term “label” can be changed to be more appropriate to what you are using it for, like “Plots”. The colour part of a label can be used in the interface. If you check in the sub-menu that I mentioned you’ll notice there are a number of different things that label colour can tint in the interface. Index card is just one of them. So it’s not (pedantically) accurate to say that label equals index card background colour, for it may not do that, or it may do other things as well.
Thanks again, Amber. I’m still at the “getting to know you” stage with Scrivener. I appreciate your help!