If the person only wants a white cat, it's their loss. How long has this cat been at your house? It might be that you haven't give them enough time to get to know one another. And, did you introduce them gradually? That might be your main problem. It does take a while, especially if the first cat has been the only cat in the house for a long time. Try putting kitty #2 in a room by himself with a cat box, food, water and a radio playing classical music. This will give them both a chance to sniff each other under the door. You can also put kitty #2 in a carrier in the middle of the room and let kitty #1 approach it. This will protect #2 from being hurt if there is a conflict. Also, give them both treats at the same time. This will show them that you love them both. Patience is the key. Then, let kitty #2 out of the room while supervising them. There will be hissing and growling which is normal. Never leave the two alone together without someone to supervise them. If, after a while it still doesn't work out, you can place an ad in the local newspaper. A word of caution. When placing the ad, ask for a donation of at least $20. The reason being is that there are alot of research laboratories looking for cats in newspapers, on bulletin boards, etc. They will not pay for a lab cat. These people can be real slick so be careful. I've seen it where they will come to your house all decked out in their Sunday best telling people what they want to hear about wanting a nice cat and it will have a good home, etc. Insist on a donation.
Please try the first suggestion. You might just be surprised. Good luck!