Wood has been a top choice in cabinet doors as long as furniture has been made. From the cabinet maker's point of view it's versatile, easy to work with, and has the ability to take on a multitude of finishes. From the consumer's side - the warmth of wood is a pleasing addition to any decor. The durability and timelessness of wood also gives it some permanence in your kitchen - if done well, a wood kitchen will stand the test of "design fatigue".
Each and every piece of wood has its own unique characteristics that makes it distinct from another. Trees are affected by the environment in which they grow. Minerals within the soil can result in colour variations withing the wood fibre. Grain patterns are a consequence of the amount of water a tree receives and the effects of the elements on that tree. These natural occurrences create a natural beauty within the wood used for cabinet doors, but also make it impossible to create a kitchen that is perfectly matched in grain and in colour.
The Heart-Birch door shown above illustrates in dramatic fashion the mineral variations mentioned above. Notice the colour variation between the frame and the centre panels, and even within the frame itself. You'll also notice the knots in the upper panel that give this door a very rustic appeal.

The doors above are from a display in our showroom. They're made from Black Walnut and show what natural light can do to a door over time. The doors in the background our exposed to the light in our front window, while the dark door in the foreground is showing the backside of the door, which is "behind closed doors". While not all colour changes are quite this extreme, they are inherent in all wood doors.
To get a full appreciation of all the species of wood available for your kitchen, it is best to come see them for yourself. Contact one of our designers for an appointment or drop by the showroom.