To my right is Chanel Azure. To my left is YSL Bleu Cosmique. Are they dupes? No. Are they related. Maybe. Sorta. In a round about way.
If you want to read the reviews here’s Chanel Azure and here’s YSL Bleu Cosmique.
Now onto the colour comparisons:
When you don’t have the bottles directly next to each other and you are going from memory you start to think that they are dupes or at least very closely related. When you have them next to each other (as above), you realise that you’ve gone wacky for even thinking about it.
In the pic above, I have my index finger and my ring finger painted in YSL Bleu Cosmique and the rest of my hand painted in Chanel Azure. As you can see the Bleu Cosmique is clearly more blue vs Azure being more green. Now when you start moving your hand you can see that some of the colour angles can make the green tones come out of the Bleu Cosmique and some of the blue tones come out of the Azure making the colours look quite similar. The differences are then the shimmer formula where YSL is definitely a more tightly packed, almost metallic polish and Chanel Azure has a lot more micro glitter and micro shimmer that is suspended and visible in the formula.
Either way, they are both quite different so if you were umming and aahing over whether to purchase these, you could justify that they are different to yourself. I did.