Question on White and Green Cards for Instrument Flying

[Locobuster]

I hope this is the right place for this, if not, moderators please feel free to move it to the appropriate one.

While doing some research I have come across several Korean War-era pilots being mentioned as having white or green cards in regards to flying on instruments. My question is were these cards a refection of their level of proficency and, if so, what were the criteria for each level?

Also are the cards still in use today or have they been replaced with something different?

Thanks in advance for any help!