It's this idea I came up with while cleaning my shelves today.
Basically, a guy has been married for a few years and finds that his skin is gradually becoming bluer and bluer.
His wife does all the cooking, and she often makes delicious stews for him that she barely touches herself, citing fullness. She also bakes cookies and brownies that he constantly takes in to work, and brews his coffee in the morning, although she always sticks to tea.

It turns out she's been dumping massive amounts of colloidal silver into everything she feeds him. Colloidal silver, in large enough quantities, does turn people's skin blue.

The problem is, I need a motivation. I was thinking she would do it just out of some form of sociopathic curiosity, and maybe has a history of conducting long-lasting "experiments" on other life-forms, such as siblings and pets.
I need ideas for some of these "experiments", feedback on the solidity of the basic plotline, maybe even a stronger motivation (although the experiment thing is why I would gradually turn a loved one a different colour, if I ever did).

Of course, the title is going to be a horrible pun, "How John Dinsmore Got The Blues". The wife's name is Matilda.
She breeds rare parrots for a living and is a kleptomaniac, so the massive quantities of colloidal silver either stolen or payed for by the birds.

Thanks in advance. Anybody who gives me an idea I'll use gets...um...recognition, good karma, and five internets.