How can you tell the difference b/w a dark lav and light purple?

[Ivanator]

Title pretty much says it all. I've been seeing a lot of purples for sale, but honestly, IMO, they look like lavs and I've also seen a few lavs that were so dark, that they look like purples. I was told by Tim at prehistoric pets that it has to do with the stripe on the head and showed me some examples, but I just couldn't see it.

[Will0W783]

Purple albino retics generally have black pupils and orange-red eyes. Lavender retics will have red pupils, from what I understand. I've had two lavs and two purples, and this held true for them all.