Due to a problem with the Color Space Converter II (CSC-II) in Quartus® II version 14.0 and upwards, you will see saturation on the output if you attempt to convert a wider bits/pixel input to a narrower bits/pixel output. For example, attempting to convert 10bits/pixel YCrCb to 8bits/pixel RGB will show this problem.
To workaround this issue, use the same widths on both input and output, and then discard the least significant bits (of each field) of the output to create the width you desire.
This is scheduled to be fixed in a future Quartus Prime release.