What is Grue emeralds in philosophy

Grue emerald is a hypothesis to prove that we cannot conclude any facts.

Explanation:

For example; the color of the emerald gemstone is green. But it may be possible that the color of emerald is not green but grue. Grue is the color that appears green before the time 2100 and changes its color after this time.

Hence it supports the both statement that emerald is green and emeralds are Grue. It is called the Grue paradox.