Grasshoppers are usually green, brown or a combination of the two. The colours help to keep them hidden in their grassy habitat. Sometimes there's a bit of orange or red but in most species of grasshopper this is hidden on the lower half of the abdomen where it won't be seen by predators overhead.
Pink or purple is not an ideal colour for a creature which lives in a green habitat. It's thought that the colours of these grasshoppers may have been caused by a genetic mutation, similar to that which affects albino animals.
In some cases the pigments are reduced, and in others there is an excess of pigment. Here the red pigment is excessive causing the colour.