It is possible to use food coloring in white chocolate if you use the correct type of coloring. When using food coloring in white chocolate, use an oil- or powder-based dye.
Water-based food coloring should not be used to add color to white chocolate because doing so may cause chocolate to seize. If an oil-based food coloring is used, adding too much may cause the chocolate to have a bitter taste. Make sure to carefully follow the directions on the packaging of the food coloring for best results. When adding the food coloring to melted chocolate, be sure to add a little bit at a time and stir gradually. If a dark color is desired, purchase food coloring that is slightly darker than the color.