The pop diva is convinced mauve-coloured foods like red grapes and plums - known for their anti-ageing benefits - will stop her developing wrinkles.
The songstress, who devised the diet with her nutritionist, now munches purple meals three days a week.
A source is quoted in Britain's The Sun newspaper as saying: "It sounds off-the-wall but it's a huge injection of healthy food in one go. Purple products are nature's best weapons in the battle against ageing. There's a saying that 'a plum a day keeps a facelift away'." "Purple food can prevent breakdown of collagen and slow the wasting of muscles." It isn't the first time Mariah has tried a bizarre diet.
Earlier this year, it was revealed she was living on plain fish and soup in a bid to shed her excess pounds.
The curvy star took all calorific treats off the menu until she reached her target weight.
She admitted she had been on a "really bleak diet, which is basically just soups and fish prepared really blandly".