As Jim says, the descriptions of the Colors is listed below your Chart, but, what is said there, does not comply to what I have found to be true.
The statement in the "Green" section, says that one should be able to receive those channels with an Indoor Antenna. That is NOT so ! In fact, one may not be able to see ANY of those channels with an Indoor.
Please understand, I am speaking from my personal experience, and no doubt there are exceptions to anything I am about to say here.
First of all, I believe that the TVFool Chart is the MOST diagnostic of any of the Transmitter Locaters, and when making a recommendation for an Antenna, I insist on having that information available to me. BUT, it's the information in the Chart that I look at, not the colors. For all practical purposes, though it makes the Chart very appealing to look at, the Colors are useless.
So, in telling you what not to pay any attention to, maybe it's in order that I say what is of importance. One may question the order in which I place value, and in fact each item is no more important than another.
The Channels are listed in order of their Strength:
As you can see from the Chart, the channels/stations are listed in their "power presence/strength" at your location. See the column titled "NMdB". This is a calculation done by the software, taking in to consideration, the KW output of the Transmitter, it's distance from you, and any obstacles which may be in the way. This has a way of falsely creating the impression to the viewer, that the station listed at the top of the list, is the one which he will receive the best.
Again, this is not necessarily so. It may in fact be the strongest, but, there are other considerations which influence how well/strongly it shows up on your TV.
So, how does that happen...
In explaining that, one must detail the information in the Chart to some degree, and the first thing one should consider, is IF you have the right antenna, to get the channel, and is that Antenna designed to receive that specific frequency well enough, to actually present the channel as the strongest. I'm referring to the channel listed at the top of the list, for instance.
The numbers listed in the "REAL" column of the Chart, are the channels that your Antenna MUST be able to receive. Since the Changeover, many find that they do not have the proper Antenna, therefore channels they once received well, are no longer available. That doesn't mean they aren't there, it's just that things have changed, and they may need to do an upgrade/change to a different Antenna. Additionally, the numbers in the “REAL” column, are not necessarily the ones which you enter on your Remote/Tuner to watch that channel. Most channels are “Re-Mapped”, and that is why there is a difference. The Antenna receives the information on one frequency, but, you have to enter an entirely different number to watch it. Don’t worry about that though, when you see your TV Guide, it gives you the correct channel number to enter, to watch it. So, the consideration of the Re-Mapping issue, only need to be observed, in the selection process of the Antenna. Once that is done correctly, you don’t have to worry about it again.
The next thing is Distance. If the Antenna won’t “Reach” out far enough, then for all general purposes in Digital Reception, the channel is not there. Back in the Analog days, one could receive a very weak picture/sound, and under some circumstances, continue to watch it. Not so with Digital, if the signal drops below a certain level, the receiver will simply shut it off, and possibly make you believe it is not transmitting.
There is other criteria concerning the Antenna, such as “Gain” and “Directivity” but one feature is very subtly included, and can vary greatly between one antenna and another. Not all Antennas receive a given Channel as well as another.
Usually because of design criteria for an Antenna, and, that design which is protected by “Patens”, one manufacturer is forced to change the design, just to provide the consumer with “their version” of a product. So, one must consider these strengths and weaknesses, by looking up the “Polar Graphs” for a specific antenna, for a specific channel.
Now that I’ve made this large literary circle, let’s get back to the “Strength/NMdB” !
So we have a certain strength channel, who’s signal is increased or attenuated by how well the Antenna, because of its design, receives that certain channel.
THEN, one must consider the System Loss because of Cable Length, quantity of Splitters, and other “dB Absorbing” features which are inherent in any distribution system. Even Coaxial Cable can affect the strength of certain channels, letting one come in strongly, while it suppresses another. This collection of the reduction of signal strength, is what causes the “order” of the channels by strength, not to be very reliable on the Chart.
One other feature, not any less important, is LOS (Line of Sight).
As it implies, indicates if your location is in direct view of the Transmitter. This has to do mainly with the Height of your Antenna. Most would agree, the higher the better, and many instances of the 1Edge, 2Edge and Tropo ratings for a given channel, can be overcome by additional height. Those imply that your Antenna can’t see the Transmitter because of terrain or obstacles which are in the way.
So, LOS is good, the others are NOT so good, and you can move from a 1Edge to a LOS for a channel, usually by increasing the height of the installation.
TVFool somewhere says that one should be able to receive any channel with NMdB greater than 0.0.
I have found that NOT to be true too. I have found that it takes a minimum of 50.0 NMdB to reduce pixelization, freezing and sound dropouts sufficiently enough, to consider that channel “watchable”. That 50 would migrate toward the 0 mentioned, depending on how “efficient” the system is.
So, don’t pay much attention to the Colors. (didn’t I say that already)