Beyond a dichotomic approach to concepts: the case of colour phenomena
  The research documents the impact of a teaching experiment designed in order to make students consider not only the spectral composition of light but also its intensity when they interpret colour phenomena. The analysis of eight recorded and transcribed teaching interviews conducted with third-year university students indicates that the comprehension of the colour vision process benefits from a "more or less" approach. Such an approach is likely to facilitate students' understanding of everyday observed phenomena. 
Viennot and de Hosson
physics.ed-ph