10k yellow gold sapphire buying ring

Product Name: 10k yellow gold sapphire buying ring
This is a 10k yellow gold ring with blue marquise cut gemstone. The ring was listed as topaz… but the blue is far too dark to be topaz… too dark and bright blue to even be London blue topaz. The maker is “ exquisite” and I buying search for the ring and found the same one listed as blue sapphire. I don't know if it is synthetic or natural BUT because it is so dark and I see inclusions( as seen in photos) I believe it to be natural( I am not a gemologist but I know a bit about jewelry). It is marked and acid tested 10k and signed by the maker. Please see pictures for more details and feel free to reach out with any questions.