Narchibald, I've used Watco's Danish Oil Natural for my Walnut projects and have been very happy with the results. The natural will give you lots of contrast but the also have a walnut and dark walnut DO.
I would also test on the underneath side before I put anything on the top.
EDIT: Just saw the picture of you table. No way I would put dark walnut DO on that. Go with the natural. I used natural DO on my
workbench made with maple and cherry. While it "yellowed/darkened" the maple a bit, I think there is plenty of contrast.
I've used their Teak Oil on Mahogany with mixed results but not on walnut. Two times it produced really nice
results and once it flopped.
Do have you have any DO you can try on the walnut? Are you going to just use DO or are you going to final coat with something else? That will change how the oil looks as well.