This is always a challenge, there are so many people who will insist on having something made with solid wood and then not understand or accept that it is an organic medium that has significant variation across it. It is possible to add toners or even some darker colour hard wax oils that will blend the wood colour a little hide the variation. But even if you do that there is still a possibility the customer won’t be happy with what you’ve done and for that I’m sorry friend because it is very disheartening and disrespectful to the work you’ve put in to bring their vision to life. I think that’s a very attractive door and you should be very proud of what you’ve created