Welcome to TeaChat!!!
Color is not a reliable indicator. Aroma can be a better indicator. Timing the brew and some trial and error is the best way to decide when your tea is ready.
Generally, microwaves are not the best way to heat your water for tea. I recommend a kettle of some kind, either stove top or self standing elictric kettle that you plug in.
Teas like white are best consumed as soon as possible after brewing, the brew tends to oxidize/darken after brewing, particularly for whites it seems to me, perhaps because white leaf has not been oxidized and is the least processed of all the different tea leaves.
However, you can rebrew the leaves throughout the day, and I have kept white leaves for resteeping even the next day.