Like Terrell, I too am a broadcast engineer and used to do transmitter alignments at a CBS affiliate. I ASSURE you, broadcasters do not let visual carrier current go to 0. That causes out of channel splatter which gets the attention of the FCC real fast. Michael also points out that a very likely culprit is AGC setting in the receiver which can cause carrier clipping in the receiver (made worse by frequency response errors in the receiver) which is exactly the same as transmitter overmodulation.. A much less likely issue would be ICPM of the visual carrier. ICPM is Incidental Carrier Phase Modulation. The PM of the visual carrier adds to the FM of the aural carrier and can show up as the field rate (60Hz) buzz. If that were the case, a separate carrier receiver (Sony VTX-1000) would have no buzz but an intercarrier receiver (almost all receivers) WOULD have the buzz. If 1 TV has no problem, the broadcaster is not at fault.
Your description of the color is correct but nobody allows subcarrier over 110 IRE. The Harris (Gates) transmitter I worked with would not go below 3% carier regardless of the input signal and would default to 70% power with no video at all. I'm sure other manufacturers do this as well. Nobody wants to be on the bad side of the FCC.
Get a DTV receiver and have a feed in your living room as good as I see in a commercial video duplication house from Digital Betacam (std def component digital)and Panasonic D-5 (HD). 100% colors are legal in the digital world. You'Il see color ranges you cannot have with analog transmission. I promise you won't miss analog.
GG