I don't think it's a coleus. That looks more like a Perilla frutescens, a member of the mint family. Does it have a fragrance?
They are considered a perennial in zone 10-11, annual elsewhere. It's reported to freely self-seed in the garden. I suppose you could collect seed and sow them the following year after last date of frost. You could also overwinter the pots inside and also take cuttings.
Here is one from our database, not sure if it's the same variety.
Beefsteak Plant (Perilla frutescens 'Atropurpurea')
