sorry if these were mentioned already, but these are mine:
if you have LIght Flush, you don't need Petticoat (although Petticoat might be peachier, but on me -- NW20 -- they are very similar)
if you have Utterly Frivolous, you don't need Strawberry Blonde (i have both, and on me they are almost identical, UF a bit brighter maybe)
if you have Black Tied, you don't need the Smoking Eyes Quad (umm the warm one? with the black shade -- smoking? -- that has multicolored sparkle. comes out looking almost exactly like BT)
i'm sure there's more, but my brain is not functioning today. i need naps!