Thank you for the explantion
I thought the colours meant something else as I've not seen that on any other lenses. I was experimenting with this lens last night and I have to say I like it. Having to adjust it manually is helping me understand how things work better than the electronic kit lens. I do have to master the art of standing stock still though...!
It's reassuring to know that it's a decent lens, thank you. A 24mm Tamron also came with my camera, so I'm looking forward to giving that a try too.