Re: Difference between BUFFERED and True Bypass......
The other explanations are good but I'll try to simplify it a little while being technically accurate. In short, the statement you made that "true bypass has no tone coloration" is actually not true, because of the way that real-world conducting materials work.
Quite simply, your guitar's signal path, from the pickups to the tone-shaping controls through the cable into your pedal board and from there to the amp, is not all built from room-temperature superconducting materials. Sorry about that. The electrical path to your amp is primarily copper, with a healthy dose of zinc, chrome, iron, tin, silver, aluminum, and a few other conducting metals. All of these are not perfect conductors; they have a range of properties that "impede" the flow of electrons and thus reduce the energy transmitted through them by "wasting" some of it as heat or electromagnetic interactions. The amount by which they do this is called "impedance", and is measured in ohms.
The first property, and the most familiar to people who paid attention in elementary school science class, is resistance. This is basically "friction" in an electrical circuit, and is a property of the conductor that resists any transfer of electrons through it, reducing the flow of current at a particular voltage potential.
If these terms confuse you, think of the circuit as a water hose. Voltage is analogous to the pressure at one end of the hose. Current is the amount of water flowing through the hose, and resistance is basically the combinations of things inherent in the system that reduce the flow of water, such as a narrow-diameter hose, a rough interior surface, blockage or kinks in the hose, etc that require more pressure to produce the same flow of water as a hose (conductor) with less resistance.
Two additional components of impedance only matter to alternating current, where the direction of the flow of electrons within the conductor changes at some arbitrary rate. First is capacitive reactance. Back to our hose analogy, conductors have a property called capacitance that is like the water hose being made of an elastic material. As the pressure increases, the hose will swell, holding a larger volume of water within it than the amount flowing through it at any given time. Back in the electrical world, capacitance is a conductor's ability to store a charge of electrons given a voltage difference between the ends of the conductor. Now, if the conductor stores these electrons, they aren't flowing through to the other side, at least not as long as the voltage remains constant. If the voltage changes, however, those electrons can "drain" from the conductor and maintain a higher flow of current for a little while. When you apply this to a system where the direction of flow is constantly changing, and so the voltage across the wire is constantly changing including an instant where it's zero, then the charge being stored in the conductor is constantly being built and discharged. This has two main effects; first, the charge that is soaked up as voltage builds and then released as voltage drops causes the change in the flow of current to "lag" behind the change in voltage. Second, the slower the change in current direction (the lower the frequency), the more charge can build up, so the energy loss through the conductor is higher at lower frequencies.
Inductive reactance is caused by a related property, inductance, which is the ability of a conductor to store energy in its electromagnetic field. This is a little harder to bring into the water hose analogy, but consider that in the middle of this hose is a piston with zero mechanical friction. Water flowing through this piston's cylinder will raise up the piston against the force of gravity; the higher the pressure, the more the piston is lifted. Now, we put this into a system where the current changes direction. We find that as the pressure builds on one side, the piston rises, but then as the pressure declines on that side and increases on the other, water flows back out of the piston shaft in the new direction of current faster than the inlet pressure would normally create. So, the flow of water from the outlet of this hose "leads" the change in pressure input into it. Similarly, in an inductor, the energy of the moving electrons is harnessed to produce an electromagnetic force, and as the current changes direction, this electromagnetic field strengthens and weakens, producing its own "electromotive force" (voltage) on the electrons in the conductor, which causes current to "lead" the change in voltage from the actual voltage source. This also produces a similar "impedance" to alternating current as capacitive reactance, but this "inductive reactance" has a greater effect as frequency increases; the amount of current flow lost to this building and discharge of electromagnetic field increases the faster the direction of current changes.
All of these contributors to "total impedance" of an AC circuit are non-zero in any real-world conductor, and so they have an additive effect as the total amount of conducting material in the circuit increases (which is primarily due to the total length of the circuit). So, as your signal chain from guitar to amplifier increases in length by adding more pedals and longer cables, total impedance of the circuit increases. This has three effects: overall signal voltage decreases, requiring more gain at the amp; capacitance increases, reducing the presence of low frequencies; and inductance increases, reducing the presence of high frequencies. So, the longer your signal chain continues as a single circuit, the weaker your guitar's signal will be and the more middy (nasally) the tone will be. This is the infamous "tone suck".
To prevent this, some pedals have an "impedance buffer". Essentially, they divide the signal chain in half, creating two different circuits, and present an impedance "load" on each side that is consistent with what the other equipment on that side of the circuit was designed to work with; so, a buffer "looks" like the front end of an amplifier to your guitar (about 1-10 Mohms of impedance), but more like a guitar to your amp (about 100kohms impedance). This is accomplished in most examples using an "op-amp" similar to the one behind your amp's pre-gain control, in a specific configuration called a "unity amp" where the input signal isn't noticeably amplified, but the use of the amplifier's power source to generate the output signal creates the two differing circuits with the varying impedances. This buffer also means that in theory it doesn't matter how many pedals exist in your chain; because each one is buffered and therefore its input circuit originates at the previous pedal, the impedance through the chain is nromalized whether you have one pedal or ten.
However, there's a tradeoff. This "impedance buffer", like any conductor, has nonzero impedance (in fact it has quite a bit of it on either side, as I mentioned). That means it has its own capacitance and inductance affecting your tone. So, the overall quality of your signal chain and resulting tone is now dependent on the design and implementation of this buffer stage. Early impedance buffers were very colored and noisy, leading many to prefer true bypass pedals. Buffers in more modern pedal designs are of much better quality, transmitting the signal much more transparently, but they still aren't 100% perfect. Second, the output impedance of most buffers is based on the op-amp used, which by happy coincidence is "close enough" to a guitar's natural load. Depending on the pickups and the settings of your volume and tone controls, it can actually be much lower, and so a single buffered pedal can have a noticeable effect on tone simply by changing the downstream circuit impedance to something very different from your guitar and one or two true bypass pedals.
