Color Hair at the Ends Only
A: Depending on the length of the hair, this type of hair color application could be as simple as dipping the ends of the hair into the color mixture to the depth of the area to color.
I would recommend a balayage (freehand brush) technique, executed in the same way you would cut a bob. Section the hair and clip it up (out of the way) except for a one-inch perimeter at the bottom. Use a brush to apply the color formula to as much of the ends as you wish around the perimeter.
Lower another segment of hair, being careful to comb it out before letting it fall to join the first section. Use a separate comb to then comb the sections together starting at the point where the color was applied to the first section. Then, apply the color mixture to the new section.
Repeat this process until all the hair is down and the color is applied where you wish. You will need to work quickly to prevent uneven processing, and you must remember to keep the "dry comb" – for smoothing the segments as you lower them – separate from your "wet comb" – for lining up the new segments with the previous color application segments – to avoid spreading the color beyond the desired areas.
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See also:
How to color hair
How to section hair when coloring
Advanced hair coloring techniques
What is the difference between regular highlighting and balayage?