Coloring or Shading

Some artists will call shading “coloring”, while other artists will
tell you that the two are not even close to the same thing. It is
this author’s personal opinion that shading is defined as achieving
any gradient or filling that is not obtained by use of a single
solid pigment. I would define coloring as using a single color
(could be multiple pigments mixed in the ink cap) to solidly fill
in a selected area. This might seem like a subtle play on words,
but it is very important as far as tattoo technique is concerned.
Even though I define coloring and shading as separate techniques,
they both are different than lining. This is why they are
so often lumped together.