It is natural for there to be some variance in the shades of green from plant to plant and even on the same plant. In many cases — including yours, I suspect — you can tweak your plant’s color by making slight changes in its sun exposure. Christmas cactus likes bright light, but can be bleached by too much direct sun. As a first step, I’d try lessening the sunlight it is exposed to and see if that gets it headed toward the darker green you are hoping for.
It is natural for there to be some variance in the shades of green from plant to plant and even on the same plant. In many cases — including yours, I suspect — you can tweak your plant’s color by making slight changes in its sun exposure. Christmas cactus likes bright light, but can be bleached by too much direct sun. As a first step, I’d try lessening the sunlight it is exposed to and see if that gets it headed toward the darker green you are hoping for.