Hi there
So, I tested both of them today in various daylight conditions:
The black one shows fingerprints and dust in bright sunlight very well
In bright sunlight the grey is easier to read but afternoon reading shows that the black one has a slight darker font.
If you compare it with the black frame the font is still "dark grey".....but darker than the silvergrey fonts.
The silver-grey material look in daylight better too.
Conclusion: I will sent the silver-gray back, keep my old K3G Keybord, keep the new K4B and cancel the KPW preorder.