There are 4 different blue hypalon colours that we stock at RIBstore: Ibiza Blue, Alpin Blue, Ocean Blue and Dark Blue.
Thankfully 2 are very distinguishable - Ibiza Blue is rather turquoise and Alpin Blue is a bright sky blue.
Ocean Blue and Dark Blue are much closer, but it is still possible to tell them apart. Ocean Blue is almost certainly more popular and as you can see Ocean Blue is also a fair bit lighter than Dark Blue.
I hope this comparison photo helps!