Minecraft Commands – How to Make the Tellraw Command Read from a JSON File

That command, while valid JSON in itself, makes absolutely no sense in the context of Minecraft.

JSON works by assigning values to specific keys, e.g. the "blue":"#3" in your command assigns a value of "#3" to the key "blue". What happens with the JSON is determined by the interpreter (in this case: Minecraft), which knows how to process certain, specific keys. "blue" and "LED TV starting" are not valid keys in this context, and are simply ignored by the game, hence the error.

An example of valid JSON within the context of Minecraft tellraw would be

{"text":"Hello World!","color":"blue"}

In this case, the keys are "text" and "color", both of which Minecraft knows how to process. There are many more valid keys, such as "bold" or "clickEvent", all of which pose limitations on their values as well (e.g. "color":"banana" doesn't work).

I suggest looking at automated JSON generators like the one on minecraftjson.com and play around a bit. Once you have seen a couple of valid Minecraft JSON, you should be able to understand how they work and creating your own by hand will be much easier (or just keep using a generator forever).

I would not recommend storing it on a USB and playing the game from there. I would recommend transferring worlds when you need to switch computers (I'm sure you can write a script to transfer files from the USB onto the computer or the other way around). However, if you must, i would recommend looking in the Minecraft launcher settings. I am fairly certain you can change the source destination folder in there (along with allocated memory to the game and other semi-useful tweaks).

This guide may be helpful: https://www.pcsteps.com/1346-create-portable-minecraft-usb-stick/