I, too, have a Marshmallow!!!
She was born all white and the back of her head looked so much like a marshmellow that that is what I named her.
A few days after her birth she started changing colors.
She ended up being a seal point Siamese(part).
I call her "Marmie". She has a sister who was born all white too but she ended up looking more like a snowshoe Siamese.
Your Marsh is quite the looker, isn't he? He is beautiful.