wrong color of gray card

[Ninanoki]

I've bought two gray cards but they have different colour. which one is correct?

 

[PRESTON]

from what I know the gray cardboard for film is a little darker with digital machines, the slightly lighter one is fine

 

[Dormeur74]

For white balance, there is no wrong cards. But these cards must not be used to measure the reflected light. To have a good reflectance card you need a card like the Kodak 18% chart which reflects 50% of the light. These are quite dark like the card on the right. White balance cards are interesting when their Lab values are known.
Hope you will understand my poor English.