Teflon is available only snow white, from what I saw. It's very costly if you need some big piece. It's indeed very slippery but way too soft for a hard mechanical contact like the sliding patches in a telescopic boom or a guide for the logs, planks and final products.
It looses its shape easily under load and you can indent it with a nail no problem (the finger nail, not the steel one !).
Polyethylene is widely used to keep moving the sliding parts and products. There are many grade to match the different industrial needs.