Strawberry is red in colour due to the presence of the pigment anthocyanin. These pigments are made in plants by combining of a molecule of some type of sugar with a molecule of an anthocyanidin.Strawberries become red only during their ripening process during which sugar becomes  concentrated in the fruit. The peel of strawberry shows the red colour due to the presence of anthocyanin pigment  when observed under the foldscope .