According to the RHS, Lily Beetle does not attack or damage Alstroemeria - they stick to the Liliaceae family, which means Lilies, fritillaries and Cardiocrinium. Alstroemeria is not a lily at all, and is not part of the Lily family, so although you may occasionally see a beetle on there, it's not a food plant for their larvae.
Slugs and snails may decimate plants in a bad year (and it is a bad year) and swift moth larvae may eat the roots.

Don't know about them changing colour, but they sound lovely, where did you get them? Have you put a pic on the site?

Thanks for the information on Lily beetle. I now won't have to buy suitable pesticide. I am almost certain that it's mouse damage so I'll have to press on with that battle.

I'm afraid I didn't take photos last year, but I bought three plug plants on ebay (£14.50) from futureprimitiveplants. I see they still have some for sale and there is a photo with them there. Last year they made quite big plants and flowered the same year. The flowers are not as showy as most varieties but the plant is covered with them and they are superb - make great cut flowers. Hope you like them