Ok before you run out and buy so called "Walnut" stain you have to know what you are working with. The pictures show weathered aged or wood. If it is natural aging or fake iI can't tell from the picture. What they don't have is a simple stain applied to them.
First you have to know what species of wood you are staining? Are they new wood or old? If they are simple Douglas Fir they will not look anything like the picture when stained. Soft woods blotch when stained.
Second the name "Walnut" will be very different from mfg to mfg and also when applied to different woods. Then there is gel vs stain. Are you applying one color or layering the stains?
If you are looking at an aged look there are tons of concoctions of the net to age wood to give it that gray undertone.
The simple way is to soak steel wool in vinegar. This when applied to D Fir will turn it a dull gray black almost instantly. You can then layer your stains or clear coats on top.
Go with a General Finshes gel if you want an even dark color which in my opinion would be a mistake. I would start very light and layer your way up. Woods darken over time so keep that in mind.
You need to practice on a close piece as everything will effect the final color including the type of clear coating. Use a dead flat clear as sold by GF. Too many variables to give specific advice. Hire a pro!!
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Floor color
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