Mr Color uses a lacquer base and is not like a conventional acrylic. Water and/or alcohol (as in Tamiya X-20A) will not work.
A lacquer thinner like Tamiya lacquer thinner or Gunze's Mr Color thinner is recommended, though generic lacquer thinners will also work (but which may be harsher). Tamiya's and Gunze's lacquer thinners are formulated for styrene and will not usually dissolve the plastic.