Your answer gives me a reason to climb back up on my soapbox and mention something to those folks who are new to working with Walnut (or any wood for that matter).
When you file or sand Walnut the resulting wood will look very light. Much lighter than one would expect to see for something made of Walnut.
Looks are sometimes deceiving.
In reality, there is often a lot of grain figure hidden right before your eyes.
Before going down to the local hardware store and buying some Walnut stain or something similar wet the bare wood with water.
It will instantly darken, some areas more than others. When it drys out it will once again look light and plain.
That "wet look" is exactly what it will look like when it is oiled with a clear oil and once oiled it will stay looking that way.
If your working with Maple, wetting the wood won't produce any large change of color but for you folks who have a Curly Maple blank, wetting the wood will show you exactly what color the wood will be if you don't use a stain on it.
Stains will bring out the curl in Maple because the wood where the curl is will absorb more stain than the areas between the stripes.
Stains on Walnut on the other hand tend to cover up any contrasting look in the woods grain pattern.