Pour coffee on it
Make a small cup of very strong coffee and apply it to the scratch with a soft cloth. This should stain the exposed wood to the darker color of the finished wood.
Color it in
Hide the scratch by rubbing it with a little shoe polish of a matching color. Alternatively, try an eyebrow pencil—soft, oil-based, and brown colored—ideal for camouflaging anything from small surface scratches to deeper ones.
Fill it with crayon wax
If the scratch is deeper, raid your children’s wax crayon set. Grate part of a crayon into a small bowl; rest the bowl in a pan of boiling water to melt the wax, then drip the wax into the gouge, smoothing it with a flat knife. You can mix a color to match your wood by adding shavings from crayons of several colors.