This has literally been debated for years and rather than explain it all over again the best thing is to refer to the neutral gray thread.

And as he stared at the gray threads, they died.

He shook his head, flashing the iron gray threads of hair at his temples momentarily.

The gray threads on his temples were becoming noticeable.

This morning I found three grey threads in my hair.

A gray thread of smoke rose from the glow.

Higher than the central mountains they stood, and the streets of Ampridatvir were gray threads far below.

The gray threads in the tentacle glow as if with sudden fire.

If a blue suit he's considering has a gray thread in it, call it gray-blue and hope for the best.

Here, embroidered lines, worked in black, gray and metallic threads, trace the grains of wood.