CUSHIONAIREWomen's Cushionaire, Luna Low Heel Slide Sandals Black 6.5 M

What’s the difference between the black, black nappa, and the black oily colors - anyone know?

Should I size up a full size or a half size for these sandals?

Can you slip these sandals on without using your hands?

Are the walking tread (the bottom of sandle) durable, or does it wear out quickly?