I teach a scripture lesson to our junior GB girls most weeks and this week's lesson gave me an interesting tidbit for my NaBloPoMo what I've learnt today thing.
In Acts 16:14 we hear about a lady called Lydia who was a seller of purple cloth (Tyrian purple to be exact). Now purple cloth was very expensive then (maybe not now seeing as it's everywhere in the shops lately) because the purple dye was so rare and difficult to get.
From the GB notes I learned that certain shellfish were gathered and that the oils inside them were white but when exposed to sunlight they turn purple. Yahoo answers answers the question Where did Lydia in the Bible get her purple from? with lots of extra info if you're interested.