Roses are red, cornflowers are blue and after nearly a century of trying, scientists say they have worked out why.
As early as 1913, scientists found that the pigment in roses which makes them red also occurs in cornflowers and was thought to be responsible for making them blue.
The discovery was puzzling because the pigment is not found in other blue flowers.
Now, researchers at Gakugei University in Tokyo say they have worked out the molecular structure of the pigment in cornflowers and found it is slightly different to the structure of the pigment in roses.
The difference lies in the arrangement of metal ions — atoms of iron, magnesium and calcium — inside the molecule.
Writing in the science magazine Nature, the scientists said they believed they had found "a previously undiscovered type of supermolecular pigment" which explains the striking difference in color.