I found a site (http://www.diatex.fr/uk/produits/agri/ombrage.htm
) selling shade nets. And this is what they have to say or warn (darn, why now?) before buying their shade nets:
Green and black shade nets behave like filters. Essential radiation for photosynthesis is reduced.
Thus, the growth is reduced. A green and black shade net decreases the lightís quantity and spectrum quality.
White shade nets :
They decrease only lightís quantity, without altering luminousí spectrum quality. As a consequence, the plantís growth is faster with a white shade net.