I'm not sure how to answer this one as I don't really stash floss for color reasons. I BUY floss for color reasons --- that is, I NEED that color for a project and it isn't in my stash.
OK, I said I had a stash of floss and that is true but it does come back to my reason for buying. I do have a habit of wanting EVERY color in a floss type (e.g Anchor, Gentle Arts, Dinkie Dyes, etc.) but have failed miserably on that EXCEPT for DMC, where I am pretty close to having every color in most every floss type (cotton, linen, rayon, metallic, etc.) - I bought a complete range (from Herrschners) back when we lived in China (the 1990s), mainly because there was no place one could buy embroidery floss there (odd given the tradition of embroidery there but it appears not to be a hobby so there are no craft stores, needlework shops, etc --- or at least there weren't when we lived there), and I have added to it (and replenished it when needed) ever since. I do have a potential "surplus" of black (310) because it is the most often used for backstitch, and it is ALWAYS used for Blackwork and I was, at one time, doing two or three blackwork projects at a time!
Now, as for a color I absolutely adore... I never actually think of that in terms of floss. My favorite color is orange but I don't think I have associated that with stitchery in any way.
So, I guess my true answer to this question is there is no color that I absolutely adore and was to stash constantly!
And while I did find a source for the stretcher frames I need for three needlepoint kits I bought last October (would you believe, Hobby Lobby is no longer selling them?), I have yet to get out my needle and fabric and floss and start those new kits, or work on my WIPs... Lack of motivation (and possibly inertia) is the main problem here...