achromatic vs aurora-colored (US) / aurora-coloured

achromatic

adj
  • Having only the diatonic notes of the scale; not modified by accidentals. 

  • Free from color; transmitting light without color-related distortion. 

  • Containing components such as achromatic lenses and prisms, designed to prevent color-related distortion. 

  • Being achromatic in subject 

  • Uncolored; not absorbing color from a fluid; -- said of tissue 

aurora-colored (US) / aurora-coloured

How often have the words achromatic and aurora-colored (US) / aurora-coloured occurred in a corpus of books? (source: Google Ngram Viewer )