Consumer Utility Maximization equivalent of economies of scope
Nothing explicit, but I think that there is no real need for a special consumer theory...

If we see diversity as similar yet not identical products, for example red and yellow shirts, then for the theory to hold, you should have specific demands for yellow shirts and red shirts

We touch marketing basics, but this is the core element of differentiation:
Markets split into sub-markets until an imperfectly imitable product is being made, then a premium can be collected on
A premium labeled red shirt for example