Why are the hex values of 001-003 or 3FC-3FE listed in yellow or red in the Measure mode of the WFM700M?

Why are the hex values of 001-003 or 3FC-3FE listed in yellow or red in the Measure mode of the WFM700M?

The WFM700M provides a lists of the data values in hex, decimal, and binary. The data values are color coded depending on what part of the serial digital waveform they represent. Green is for active video data, gray for data in horizontal and vertical blanking intervals, white for 3FF, 000, XYZ data values in EAV and SAV, yellow for data outside nominal allowed values (040-3AC for Luma), red for data with illegal values. The illegal values of hex that are listed in red depend upon whether 8 bit or 10 bit serial digital video is being monitored. With 8 bit video only 000 and 3FF are listed in red if they are not in the SAV and EAV packets, and 001-003 and 3FC-3FE are listed in yellow. With 10 bit video 000-003 and 3FC-3FF are listed in red (when 000 & 3FF not in SAV & EAV).