Synonym for "chameleon"

I'm looking for a synonym for the term "chameleon" as applied to a person who easily fits in anywhere by altering their demeanor in a respectful positive and aware way, not with malicious intent. All ideas appreciated!

A person who switches demeanor or word choice to fit into different groups at different times is code switching in the sociological (not linguistic) sense. From the NPR article:

When you're attuned to the phenomenon of code-switching, you start to see it everywhere, and you begin to see the way race, ethnicity and culture plays out all over the place.

"adjustable" and "adaptable" (the latter mentioned in a comment by FumbleFingers) come to mind.

adjustable - able to be changed to suit particular needs CDO

• "In talking about the more adjustable personality of the middle born child..."
• "A positive, easily adjustable personality, with a streak of modesty." from Google Books

adaptable - able to change or be changed in order to fit or work better in some situation or for some purpose.

• "The highly adaptable person meets the other person's needs and his own." The Platinum Rule
• "An adaptable child learns to recognize the internal state of distress and hyperarousal, then finds ways to inhibit the arousal..." Effective Parenting for the Hard-to-Manage Child

It's interesting that you mention you don't want it to be a negative term, since most usages tend to be.

I suggest changeable

able to change or be changed

as a value-neutral alternative.