Q.  Should I cut off the flower head to keep the colour in the leaves?

A.  Flowering and fruiting is part of the natural growth cycle of cordylines, a lot of the plants nutrition is used in the flowering phase.  If the flower head is removed early it will short-circuit the growth cycle and stimulate new stem and leaf growth.  The removal of the flower head will have no effect on colour, the colour is part of the cycle in many of the cordyline cultivars and will intensify naturally going into the cooler months.