Differences in hue would be a challenge to study, which isn't an issue, just something to deal with in terms of how many differences we want. Color is sort of subjective, it seems. We could say most sapphires are plain blue sapphire, some navy/sea color, some lighter/sky color, and some really light or dark? I'd say breaking them into:

Non-magical - most common - plain sapphire
Teleport - rare - dark dark sapphire (near black/navy)
Attack - uncommon - darker sapphire
Defense - uncommon - lighter sapphire
Healing - rare - light light sapphire (near white/pale blue)

Does that work?