The values in the color tab are not representing the full range. The view in SNAP cuts off 5% of the data’s extreme values for visualization purposes to enhance the contrasts: Differences between image without and with 95% or 100%
The data’s actual value range might be considerably larger, especially when there are extremely bright pixels in the image, but these values are neglected by SNAP so that the data has balanced contrasts.
If you want to get accurate values you have to select the statistics tool 