All the guy at the nursery said was it's Joseph's Coat, you treat it like a houseplant, & bring in winter.

Pretty! It looks like this Alternanthera, or other similar variety:
Alternanthera ficoidea 'Snowball'

'Joseph's Coat' is supposedly a cultivar, but the name seems to get used as a common name for other Alternantheras as well. A search for pics of that will find many different looking leaves.

I've had a few Alternantheras, they're more amenable to coming inside for winter than a lot of other plants. It should go well if it can be near an E/S/W window for winter.

Alternantheras are tropical plants that do not do well in temps much below 50 degrees F. Indoors, it must have a lot of direct sunlight to maintain its color.