the scratchplate on my squire strat which was white before has now turned almost a darker shade of cream than the body. Although I like the old, battered look on strats, how can a make the scratchplate look a little white (but not totally birght white)

You could try a 10% bleach 90% water mixture on a soft cloth. If that plastic has fire retardants in it, that would explain the color change. Over time, fire retardant plastics turn a creme color, that's why old NES systems and computers turn that color as well.
Seems weird to put fire retardant plastic on an instrument made of wood though... :/
Most modern plastics are fire retardant.
Quote by Jim Morrison
Indians scattered on Dawn's highway bleeding, Ghosts crown the young child's fragile eggshell mind