She’s a lady in red.

Kate Middleton looked radiant in an electric blue coat dress for Easter Sunday services at Windsor Castle yesterday, but one small detail of her look had royal fans going wild.

The Princess of Wales, 41, made a surprising move by wearing bright red nail polish on her fingers for the first time in public since she married Prince William in 2011.

While there are no official rules per se about how women in the royal family can do their nails, it’s been said it was a preference of the late Queen Elizabeth II — who was a devotee of Essie’s pale pink Ballet Slippers polish ($10) — for royal ladies to sport light, natural colors.