Most digital cameras will show white surfaces as gray because they are set to underexpose the surface if they take up a large part of the field of view.
Celestron digital microscopes have auto-exposure cameras that are set to average metering for a normalized reflectivity of the subject. Usually this is set at 18 percent reflectivity–a medium shade of gray.
Another factor is the bluish light from the microscope LED illuminators, which can shift the colors of images away from their natural colors.
Depending on the model of microscope, try adjusting the gain settings in the image capture software or EV (exposure ) value offset in the digital microscope’s menu. You can use the microscope’s filter wheel for bottom illuminated subjects.
Take images against differently colored backgrounds if they take up a significant fraction of the field of view. Using different backgrounds can also change the color cast of the reflected light from the microscope’s illuminators.
Post-processing with programs like Photoshop can adjust the images to look either more natural or to your liking.