My daughters did this, think it is just something they do, last spring I chopped hers right back, it was very woody, it flowered back to its two tone colour flowers and has been amazing this summer. :O) Try it, you have nothing to lose, have no idea when they should be cut back but this was a case of trying it and hoping it worked for her, which it did.

Im sure i read somewhere that it was certain environmental factors that changed the flower colours. Flowers can either be all pink, all white or pink and white.

Mine have also turned white and i read that it was either temperature or moisture levels that determined flower colour.

Even if it is all white, there's nothing stopping the next lot of flowers turning pink/white either this year or next.

Hot Lips does this - it goes through a 'red' phase (especially early in the season), and a 'white' phase, often in hot weather. It's nothing to worry about - it will go back to carrying both colours in its own time.

My Hotlips plants new flowers are white but then turn two tone.Flowers from June to first frosts.Hardy to -5c Cut back hard in early spring,kerryvw.