The 'We Found Love' singer showed off her new look via Instagram on Thursday morning (18 July), saying: "Grey is the new black! Blondies, it's quiet for y'all! #brr."
Alongside another picture she wrote: "New colour is ice greyish, call it. #brrr."
Fans appear to be mixed in their reaction. Some love the new look, others aren't so keen. One even wrote: "Ahhh, rih rih why? It looks like a witch's wig."
Another joked: "Aww so cute, my grandpa has the same colour..."
Rihanna, 25, had blonde hair before her big change, but she's no stranger to switching up her look, having sported everything from black to brown to fiery red over the years, short, long, fringe, no fringe.
While her new grey hair is unusual, she isn't the first star to opt for a colour most frequently associated with age. Kelly Osbourne and Little Mix's Perrie Edwards have both worn grey shades in the past year.
Rihanna has been in the UK this week for several performances: first, she rocked T In The Park in Scotland as the Saturday night headliner, before travelling to London for a surprise appearance at the Yahoo Wireless Festival alongside Jay-Z.
She then played dates on her 'Diamonds World Tour' in Manchester, with another date scheduled for Birmingham tonight.
Rihanna's best bikini pictures - gallery: