One issue I see far too often, is everybody likes to default to blue insulated crimps (they're designed for 1.5 - 2.5mm˛ cable), when they should be using red ones (for 0.5 - 1.5mm˛ cable), which means they don't crimp correctly and you end up with bad connections.
For the cat5 flex I use the white But not sure if there is any stardard

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