This is the side of a walnut display case that is pretty beat up. There are a number of deep scratches that go through the finish and into the wood. The case belongs to a small poor historic society so they just wanted it cleaned up and not totally redone. This is just one way to deal with scratches. The case had tape residue and lots of grime so step one was to clean the surface. I first used a damp rag to remove the water soluble grime. I then used black light and a solvent test to determine that the finish was varnish so I was able to clean it with mineral spirits which removed the tape residue and oil soluble grim.
Display case
After the surface was cleaned it was given a coat of thin shellac. The shellac seals the scratch but more importantly it lets you see what it looks like with finish on the surface. Starting the repair this way makes it much easier to match the color.
cleaned and sealed
Next step is to fill the scratch and level the surface, for this repair I choose a hard wax fill stick. The hard wax sticks are easy to use because they melt at a lower temperature than shellac sticks, but for a table top or writing surface I would use the harder shellac sticks.
fill sticks
Both the hard wax and shellac sticks come in a number of colors both opaque and transparent. The wax sticks can be melted with a standard heat gun.
heat gun
Multiple colors can be combined, when melted by mixing and leveling with a plastic scraper or card.
fill sticks
The end of the stick is melted with the heat gun then rubbed into the scratch for this repair I used the two colors above. In the out of focus picture below [I must have bumped the tripod] both colors have been applied. Next the fill is warmed with the heat gun then mixed and leveled with the card.
fill
Here are the filled scratches.
Fill Leveled
With a coat of dye toner.
Toned
Here we see there is a dark streak that ends at the edges of the repair.
Streaks
By continuing the streak through the repair it can be further camouflaged.
finished
millcreek woodworking 
How did you continue the dark streak? Did you use a darker color of the wax or a darker stain (or something else that isn’t popping into my head right now)?
I used a little ground pigment on the end of my finger,just rubbed in and covered with the final finish. These pigments are available in many colors for touching up finishes. I don’t like to name brands but Mohawk sells one called “Blendal”.