Does anyone know if this type of fairly cheap pre-made melamine cabinets
ever come in anything other than white?

It's only basement storage so why obsess over it? Get the cheapest units trhat
solve the problem and enough cans of Krylon spray paint to change the colors.
Get some masking tape and go wild with different colors and patterns. Pretend
you're on "Trading Places" and enjoy. Good luck.

Joe