Reviews about Goldwell System Developer Lotion

I previously purchased this product in a white bottle with a mature label. I mixed the colors 4n and 4na, and on my hair, it appeared as a dark brown shade. I ordered the same product again, but it arrived in a white bottle with a black label. After using it for the third time, I saw no results. It slightly pigmented my gray hair, but it washed out within a week. Now, what should I do with this useless liter-sized bottle? I wasted my money on this product.