Thank you for your interest in PhotosRevive.
PhotosRevive has been designed to do realistic colorization. That is why the application does not allow you to choose white or black colors. The reason is that teeth are never white. The color would be a king of light gray and light yellow.
The color grid proposes 5 main colors : green (top-left), orange (top right), purple (bottom right), blue (bottom left) and neutral (center). The idea is to let artificial intelligence makes the first colorization. Then you will get some areas that are not colorized correctly. You should click on these areas. The application will display a point. The color palette will change to display only realistic colors for this point. In your example, if you click on the teeth, the palette will only show light colors. The app will never propose you black colors because nobody has black teeth. All you have is to choose a color between white (center) and yellow (top center).
The application uses the CIELAB colorspace, where the application locks the L component. You can only choose the A and B components.
I know that it can be complicated to understand at first. You can send me an image. I will make a short video showing how to make the colorization.
I hope it helps,