I know nothing about changing colors so will defer that to the experts.
However, I would do some serious soul searching to determine if you think that the color of your dog is going to influence how you feel about it. I had a friend who married a guy with a pug. She eventually gave the pug to her son because she felt it was ugly and could not bear looking at it!!!! YIKES! This is an extreme example, however we all have certain preferences and perhaps do not have complete control over them. For example, gray walls are in style...I have tried to like them but I just don’t and nothing is going to change that. I personally feel the dark faced Havanese are just as cute but they just do not come across as well in pictures. There are plenty of other colored Havanese out there. If in doubt, I would wait.
Well, I wonder what ELSE was going on that the MAN would ALLOW his wife to give his dog away, but be that as it may, there is a lot more different about preferences for breeds than preferences for color. I couldn't live with a pug for oh so many reasons that have nothing to do with color... or even looks, really.
But of course it's always possible to pass on a puppy that is the "wrong color" if you really have your heart set on something else. Honestly, I have a "thing" about really uneven markings. I don't think I could take a puppy that had REALLY uneven facial markings, no matter what the color. It's a personal thing.
Just remember that the more strict criteria you put on your puppy search, the longer it will take you to find the "perfect puppy". We regularly hear people complaining on the forum about how long it can take to find the "right" breeder who will have a litter in the time frame when they want a puppy. Almost everyone wants a healthy puppy and a good temerament. (some people put on blinders and play Russian Roulette with those and the good breeder criteria, buying puppies over the internet, based on photos, but I wouldn't advise it!) Then some people add that they want ONLY a girl, and ONLY a certain color, and that they ONLY want one small enough to fit in an airline approved carry-on... Oh, and they want it to be a show prospect... Now they are looking for something pretty specialized.
The more boxes need to be ticked, the harder it is to find "the perfect puppy".
When I was looking for my first Havanese, I'd been looking for "the right breeder for a long time. (almost a year). I found the Kings, and knew I wanted a puppy from them. I asked to be put on their waiting list. They had a litter, and then soon called me. It turned out that most of the people on their waiting list right then SPECIFICALLY wanted girls, and the WHOLE litter was boys! They asked if I cared whether I got a girl or a boy. I said I didn't care about the sex as long as the puppy was the right fit for me. The rest is history. Kodi couldn't possibly have been a better fit for me and my family! There was no choice in color, even though there were 3 puppies left when I went to meet them because all three were marked almost exactly alike! Black heads, white bodies with a single spot in the middle of the back! LOL!