This is true. Any blocking of visible light (grey tends to block cross spectrum) will diminish color recognition but grey should be better than colored shields unless it blocks too much light.
http://www.bsd-dresden.de/en I did the testing for the ASTM standard for this sheild and it also has been tested with a proposed IEC box method.
We've had them for about 1.5 years showing at some of our training classes. Pro's and cons with everything. ArcWear DOES NOT sell items. We do testing and take no commissions. BSD has advertised in our newsletter a few times but there competitors advertise more. German company. Seem like good folks.