Blue Smarties, which were introduced in 1989, were withdrawn in 2006 after Nestle Rowntree decided to remove all E colourings from Smarties but was unable to find a natural colouring alternative to E133 Brilliant Blue.
Nestle has now found a naturally occurring azure blue colour in spirulina, a type of seaweed. Spirulina is noted for its health properties, including its richness of proteins and minerals.
The company also axed four other E colourings from Smarties, including Quinoline Yellow and Carmoisine in 2006, but was unable to find a natural blue alternative at the time. The removal of blue Smarties led to the introduction of the unpopular white Smartie.
A spokesperson for Nestle Rowntree said: "We are happy to oblige now we can keep all Smarties free of artificial colours."