I have recently lost the control over how I view my image when using the spot healing brush. My photos automatically go into negative view and there is no slider for adjustments. This is making my workload impossible at times.
Sounds like you have inadvertently pressed A, which turns the image into high contrast black & white. The purpose of this is to make spots that need retouching more visible. Press A again to turn it off.
You can also turn this off by unchecking Visualize spots in the toolbar at the bottom of the screen. There is also a slider to control the contrast of the black & white image.