Clothing subscription services you mentioned, themselves advertise as fashion subscription; I guess that's because of the scale and unit economics of selling some random curated items as fashion at premium price. I personally like high quality plain T-shirt with good colors, but I wonder whether there are enough takers for 'simple fashion' as a subscription service in the country.
There are several such services in US though, DollarTeeCompany comes to mind from their quirky ads. I think, you should start speaking to your colleagues who wear plain T-shirts regularly on whether they would subscribe to a service which sends them just that and how much they are willing to shell out for that.
You could also share this need gap to those who might face this problem and bring them here for unbiased validation!