If I take a standard blue Sharpie pen and write on matte white paper, the ink appears blue as expected, as shown in (a) of the attached photo. If I write with this pen on black plastic, it appears orange (b) in incandescent, fluorescent or daylight illumination and for specular and non-specular viewing angles. How to explain this? Another observation - If I use the pen to write on glossy white paper, the ink appears blue for non-specular and pinkish for specular. This is seen in (c) where part of the writing is viewed specularly.