Image Pixel Wise Transformations - Recommended Order
Since both operations are not linear they are not interchangeable.

When Processing RAW Files from Digital Cameras you first create the correct balance between the RGB channels (White Balance) and only then work one effects like contrast.

One could use hands waiving to say that before doing contrast one need to set the correct value of the pixel (White Balance).
There is a logic to that but it is not derived from a Physical law or Mathematical truth.