I agree that a relaxed chameleon isn't grey or black. I'm saying that they are duller than their fired-up colors.
Also, I should have been more specific when describing their language of communication. Like humans, chameleons have different "voices" (i.e colors) to communicate for different occasions/events/situations. Like you said, when they are stressed and fear for their lives, they turn a darker color with stress patterns. When they are ready for combat such as fighting off another male, their colors peak in brightness. But there are also other colors/voices they have. Stress doesn't mean that they fear for their lives. Some stress can be bad but other forms of stress can leave minimal to no impact at all. Handling your chameleon every once in a while would fall into this category where they experience stress, but don't necessarily fear for their lives as you have established trust as their food provider, which has no long-term effect on their health. But this doesn't mean that they can't communicate that. They are always letting you know how they feel.
Since they have multiple voices so-to-speak, they will also communicate the "I don't fear for my life, but I'm still experiencing a type of stress." This is done by the colors that you see when your chameleon is showing bright vivid colors, but not quite fired-up. We tend to correlate these colors with them being happy because they get to explore, but this is anthropomorphizing them. They aren't happy, but they also aren't deathly afraid or preparing to fight for their territory; they are simply communicating the stress they are experiencing. They certainly aren't relaxed. We have to be careful of anthropomorphizing them.
This is a species that has developed color as a way of communication. I think we underestimate how well they have developed this trait. Different stresses result in different colors. No stress will result in basic colors. They aren't dull, but they aren't vivid. This is simply how chameleons have evolved to live. They are solitary creatures constantly on the lookout for predators and prey. They are the closest to happiness when they are in a relaxed state. I wouldn't be surprised if happiness is an emotion they lack.