First picture: It looks like it is reacting to very cool or cold conditions and preparing to go dormant. What kind of temperature exposure does it get?
It could also be due to over watering.

Second picture: Pot-in-a-pot setup is not a good idea for dendrobiums. The roots prefer the pot to dry up quickly in between waterings. That setup will retain moisture far longer than what the dendrobium prefers. It would reinforce the indications that the plant is over watered from the first picture.

Third picture: Is it a different plant than pictures 1 & 2? It looks like rot of a bacterial or fungal nature. It usually sets in when the plant stays too wet and does not get adequate air circulation.

Fourth picture: Nothing seems out of the ordinary there. New canes do appear a bit pale when very young but should green up as they mature.
The potting mix on top appears to be dry, but do check if the inside is drying up just as fast. A dendrobium pot that stays wet for too long will kill the roots.