I have read lots of good reviews of Hilary McKay's books about the Casson family and this is the first in the series. Saffy's real name is Saffron and while she is named after a color like the rest of her siblings (Cadmium, Indigo, and Rose) it turns out that they are actually her cousins. After Saffy's mother dies, her grandfather becomes catatonic and when he passes away, leaves Saffy an angel in his will. Though her father (a rather absent father) shrugs off Saffy's inheritance, she is determined to find it.
The Casson family is great. The relationship between the four siblings and the odd quirks each one has are very endearing. There is that bit of British in the story which lends it something a little extra in my opinion. I would read more about them I think.