As promised, here is a comparison post with Butter London’s newer blue shade, Keks. None of these are dupes for Keks in color or finish, but I thought this would be helpful for those wondering about different shades.
I included Slapper first, because I saw someone asking about it on another website; it is definitely not in this type of blue family and lies in the teal family.
Revlon Colorstay Coastal Surf is much lighter and has a glossy finish. Shelter Island from Essie is not nearly as opaque and is also lighter. Perhaps the most similar shade is Revlon Lagoon Afternoon, but it is definitely not a dupe.
The differences in these blues are a lot more prominent in real life; on the screen they don’t show the clear distinction between them due to the lighting! Still, the finish of Keks really stands out here. You can see the semi-matte rubber style finish.
I hope this was helpful! 🙂