Bloom Tender can't produce colorless mana, even if you control a colorless permanent.

For each color (white, blue, black, red, and green), check to see if you control a permanent of that color. You can count the same permanent for multiple colors. For example, if you control a green enchantment and a white-black creature, Bloom Tender's ability produces .

Bloom Tender won't produce more than one mana of any particular color. At most, it will produce .