Our bodies respond differently to stress; whatever the cause may be. Studies have shown that stress causes the release of the chemical norepinephrine into the follicle - and this affects the melanocyte (melanin-producing) stem cells living there, causing them to rapidly turn into pigment cells and move on out of the hair follicles. So without these melanocyte cells, new hair turns grey or white.
Silvery strands are mainly caused by the decline of pigment cells, melanocytes, and are part of our natural ageing process, which is dictated by genetics. If you choose to colour the greys, there are some great products on the market that will protect and repair coloured hair or ones that will tone brassiness and enhance those sparkly greys.