Usage patterns
灰色の空a grey, overcast sky
The sky had been grey and overcast since morning.
灰色の毎日a dull, monotonous daily life
I was living a dull, monotonous life buried in exam study.
灰色の〈人〉someone suspected of wrongdoing but not proven guilty (a 'gray area' figure)
He is being investigated as a 'gray' figure in that case, not yet proven guilty.