Fleur
It is not the colour that counts in this case, it is the leaf form.
Both S. microphylla and S. greggii have many color forms, mostly cultivars.
Often it is quite difficult to tell as both hybridize freely in cultivation. There is a natural hybrid as well, named Salvia x jamensis.
The best way to distinguish between the two are the leaves:
S. greggii has nerrower, slightly bluish leaves with smooth margins [you can notice it at the lower photo]
S. microphylla has more roundish, deeper green, non smooth surface and serrated margins
But the hybrids may have all the carachters above...