code: public void setSpecularIntensity(float r, float g, float b, float a) {
         setVec4("specular_intensity", r, g, b, a);
     }
docs: Set the specular intensity of the light.
  
  This designates the color of the specular reflection.
  It is multiplied by the material specular color to derive
  the hue of the specular reflection for that material.
  The built-in phong shader {@link GVRPhongShader} uses a {@code vec4} uniform named
  {@code specular_intensity} to control the specular intensity.
  
  @param r red component (0 to 1)
  @param g green component (0 to 1)
  @param b blue component (0 to 1)
  @param a alpha component (0 to 1)