If you know the cabinet manufacturer, door style and stain or color, it should be easy to match the cabinets, right? Well, not exactly. Even if you have white cabinets and you order new white doors, or new white cabinets, they won't match. Why? White cabinets yellow over time. Even if it's only been a year or two since the cabinets were installed and they still look bright white to you, they won't look white when compared to a new cabinet. As for wood stains, they darken over time. So a new cabinet with the same stain will not match.
Another reason we don't recommend trying to match existing cabinets is that manufacturers often change hardware. The new doors that you order for your existing cabinets may not have the same hinge placement as your existing cabinet door.
If you're adding an island or another group of cabinets to your kitchen, such as a butler's pantry, you're better off using a completely different yet complementary color of cabinet. Using the same door style will bring it all together.