My mother just told this story about her and her father (my recently deceased grandfather).
She said it was from the time when "you had to use Fountain pens, because there weren't any others."
He'd sent her to the shop when she was a wee girl to get him a bottle of ink. My mum asked him what colour ink he wanted, and his sarcastic reply was green ink. So my mum went down the shop, and bought him a bottle of green ink. As a result, my grandfather wrote in green ink for a very long time.
I'm not sure if my mother misunderstood my grandfather, or quite likely that my grandfather didn't realise that the little shop down the road would sell green ink as well as his usual black or blue and so he got stuck with green ink.