I design and sell T-shirts myself on Redbubble. Eventually (hopefully in my lifetime), online print-on-demand T-shirt quality will rival the more traditional printing houses and business model where the burden's on you to order in bulk in assorted sizes, styles and colors then stockpile and monitor inventory. You then have to make sales to recoup your expenses.
With print-on-demand (p.o.d.), nothing is created beforehand so you don't have to calculate any of the above nor worry about up-front costs or fret over stagnant inventory.
Maybe the best of all possible worlds would be maintaining just a small number of the most popular items for walk-in visitors to the Mothership while providing online access to the full line of clothing via p.o.d. This way a customer could also personalize their shirt with their name, for instance.
FWIW, I've been collecting black T-shirts for over 30 years and the best way to keep your shirt looking black for as long as possible is to always wash inside out in cold water, then hang it to air dry. I keep a rotation of about 200 functional black shirts and wash 35 in each batch. When I hang them to dry in my apartment it looks like a goth shrine or a bat cave...
