The female will take on the gravid/non-receptive coloration when she "needs" to...in the presence of a male, for instance. When she has no "need" to she may show her normal colors.
Signs that a female is gravid and near laying time include but are not limited to such things as...roaming the cage, drinking more than usual, looking wider in the "hips". She may or may not stop eating depending on the size of the clutch she is carrying and whether its fertile or not.
(She should not sit low in the cage, sleep during the day or become lethargic...these can indicate eggbinding.)