I believe in un-neutral neutrals. For years, jewel tones and primary colors formed the basis of my tiny wardrobe, which never hovered above 40 items (this includes everything- underwear, socks, swimwear, special occasion dresses, etc.). Accessories were leopard print, emerald green, and purple. I paired gingham with floral prints and floral prints with stripes.
Then I moved here, a melee of navy blue, grey, tan, and beige (I didn't know tan and beige were different, but French women made the distinction very clear; heaven help you if you wear khaki). Beyond that, Parisians' preferred colors are red, forest green, and pink. In this city, wardrobes require refinement and subtlety. The M.O. is to dress quietly, simply, never stand out too much. Subdued colors, I've learned, have the desirable effect of making clothing look much more expensive than they are.
If, like Julia Restoin-Roitfeld, you're not sure of your own taste, refer to the guide above for successful combinations. Solid colors stand repetition better than patterned materials- people are less likely to notice you have a tiny closet if you wear the same navy dress every week, instead of a fluorescent pink houndstooth one. When creating outfits, try limiting yourself to one basic color, plus one or two notes of a second color, or another shade of the basic one. If your outfit is patterned, it's best to wear accessories all in one shade, preferably the darkest color figuring in the pattern.
The concept of "seasons" is outdated and doesn't work for multiethnic skin like mine, but red and sky blue are universally flattering, and all the jewel tones and pastel shades can be mixed together. Establish your own palette, choosing multitasking shades for accessories. When adding new pieces, make sure the shade, pattern, or print coordinates with at least three items in your closet.
Never rule out trying a particular color because of some "theory." There's too much mystery around colors- with so many nuances and shades of each, one is bound to work. At the same time, it's fine to rule out something that doesn't match what you already own. Click here to read about my wardrobe, here for a carry-on travel packing list, and here for natural stain removal.