Overexposure is the effect when optical sensor reaches saturation and from that point on, only the maximum pixel value (usually 255) is shown. Overexposed objects can cause a lot of headaches in image processing, but there are ways in which it can be made useful.
Considering that prices for mono and color cameras are identical for some manufacturers, does it still make sense to even consider buying a mono camera for your application? If you are just googling for a quick solution, the answer is yes. As to why, keep on reading.