Well if you apply a dark coating, it will show any chips and scratches like crazy.
Is this "Brazilian walnut"?...not really sure what kind of wood that is...but if it isn't the color you want and you don't want to pay to have it stained, it seems to me you ought to either choose another wood, or modify your exzpectations.
Linda C

Hi, if it's American black walnut, it will tend to get lighter over time (is there any other wood that does this?) so I think a stain is very much in order. If it's American black walnut, it isn't prone to blotching. It should be sanded to at least 150, as it is a fine hardwood, not oak, it deserves the extra attention.
Casey

I can think of at least one - padauk. It starts out a bright red, then fades to a pale brown with sun exposure. Other woods that start out brightly colored will also fade with time. Purple heart is another I can think of. I've seen it tend to go to gray with time.

Black walnut starts out a moderately light purplish gray (a bit ugly in the raw), and then quickly goes a wonderfully warm brown with exposure to sunlight. IMHO, I'd never stain it, and if I did, my wife would kill me.

John

you can waterpop the floor and make it darker without stain

As beautiful as walnut (Juglans nigra) is, it is only moderately hard for a flooring wood. One of my regular clients has walnut and marble floors throughout the house. (This is one of the most expensive houses in the city, a bit north of $6m). The floor is less than 4 months old and has little blue pieces of tape all over it giving the contractor a punch list of areas to redo. Likewise the steps are scuffed and scratched.

While it may be temporary (until the wood lightens), have you observed black walnut when it has had boiled linseed oil applied? It darkens and the oil can be top coated with an oil-based varnish.

If it is "Brazilian Walnut" (a great liberty with marketing-speak), it is most likely Ipe', AKA Pau Lope®, Ipe Brazil, Amapa, cortex, Guayacan, Flor Amarillo, Greenheart, Madera negra, Tahuari, Lapacho negro or maybe cumaru (Dipterix odorata) or jarrah (Eucalyptus marginata). That would be a horse of a different color.

Here is a link that might be useful: walnut as flooring

You can use an aniline dye to stain the floor without any fear of blotching. Then do the oil. After the oil is dry you can top coat with the clear finish of your choice. A seal coat of shellac over the oil may help some top coats adhere better. An oil/varnish finish isn't really hard enough for floors, but it is very easy to repair over and over.