Clinique describes the duos as: Perfect pairings of in-demand shades, with more of the more-used highlight shade. Deliver creamy, intense colour in one stroke. Comfortably lightweight, long-wearing. Layerable, blendable.
Unfortunately, I'm not sure I agree with their description of the formula. These are buttery and soft, but sheer and not intense. It doesn't seem like the colors get more intense with layering either. They do seem appropriate for daytime wear since the colors are so subtle.
The duos come in 16 different pairings. I decided to try Beach Plum.
The gold color is a shimmery very yellow gold with decent color payoff. The purple is a sheer violet with a little gold shimmer.
These definitely perform better over a primer. The color payoff is even better with a sticky base (like a NYX Jumbo eye pencil). I get a little creasing after about 5 hours without a primer, although it is hard to tell because they are so sheer.
Without primer or base
With NYX Jumbo Eye Pencil in Milk as base
I haven't tried other colors in this line, so it's possible that they perform better than this one.