If you find a colleague who emanating very negative vibes or appears to be in a bad mood, try some of these questions or similar ones and wait and listen to the answers.
"So tell me what is great in you life?"
"Tell me something good that happen to you recently."
"What is something that you are proud of?"
"What is your favourite hobby? What do you like about it?"
"What is your favourite vacation spot? What makes it special?"
If you know something specific the person likes ask what he likes most about that thing.
I think you get the idea. When the person responds, ask for more details in a way that proves you listened to what the person said. You will be amazed at how quickly the vibes change.
Once the mood has changed to a more positive frame, you will be surprized how much better things will go.
Try it a few times using my questions just for practice. Then use your own.