Witte kernels are dark even when harvested fresh off the tree (figure left). A few weeks after harvest the kernel color gets even darker. Witte kernels also have a wrinkled "old man" appearance that contributes to an illusion that the kernels poorly filled out.
You can really see how dark the kernels of Witte are when you compared them to kernels of Oswego and Kanza (photo at right). When consumers are shopping for pecans they associate light kernel color with freshness. Dark kernels are avoided as being possibly rancid.
Because Witte produces such unappealing kernels year in and year out, I wouldn't recommend this cultivar to any northern pecan grower.