Metallic/Mica : Metallic or Mica paint usually consists of small flakes of aluminium or other metals  to give the car a metallic sparkle by reflecting the light. This shine will not change colour when looked at from a different angle. The paint hue will stay the same.

Pearl: Pearl paint contains small flakes of mica (ceramic type crystals), a synthetic material that does not reflect light, but lets it refract white like into different shades. This will change the shade of the colour when looked at from different angles. (to replicate a natural pearl)