Question: I have two signal lines, both will be running at the same time on a PCB. RGB lines running at 75 ohms impedance -0.3-+0.7v (1v). (Standard video lines). Currently both lines are active/running/receiving a signal at the same time. Lets just use two lines Red and Green for simplicity. I'm looking for a switch/or method where when Red is active, Green is disconnected. I know this is a very simple question, but I was thinking of using logic gates, but 0.7v is considered low so that wouldn't work. And from my limited knowledge I know that basic transistors only turn on at 0.6v so that wouldn't work either.

If Red is active, Green needs to be disabled. I am not using a cable. It's a PCB design. Switching needs to be done on the PCB circuit

Answer: 
A MosFET doesn't have a volt drop across the gate, but a resistance, so that would be my first thought. You obviously need an active circuit to control the switching FETs. A comparator would be my first choice to detect the Red voltage and boost it to a level sufficient for logic operations and thus control the Mosfet gates.

When Red is detected as high, switch the Red FET on and Green FET off, when it's low, Red off and Green on. You would want to select a mosfet with a low Drain-Source resistance.

This is assuming that the lines are fully on or fully off, that is only switching high and low as implied by your question.
Will this do what you want?

![schematic](https://i.stack.imgur.com/HvXgR.png)

[simulate this circuit](/plugins/schematics?image=http%3a%2f%2fi.stack.imgur.com%2fHvXgR.png) – Schematic created using [CircuitLab](https://www.circuitlab.com/)

If these are video signals, the wires should be coax cables, with the shields connected together at the switch.