This model - based on the picture of a very real grandmother - is quite forgiving. You can change the colors in practically any way you like, and still get results that look good. Just try to preserve the order: from dark colors to lighter ones.

Print at 100% infill with a layer height of 0.08mm with a base layer of 0.16mm

Filaments Used:
PLA Black
PLA Blue
PLA Light Blue
PLA White

Swap Instructions:
Start with Black
At layer #6 swap to Blue
At layer #9 swap to Light Blue
At layer #10 swap to White for the rest.