After a few days of usage, does this Steel change its Color?

No, this is 925 925 sterling silver. So the colour won't change.

What is its diameter?

The diameter of this adjustable bracelate is 7.7-8.7".

Are any other colors available?

As of now we have only color available.

Is this bracelet elasticated or just a normal adjuster?

It is just normatl adjustable bracelet.

Is it really Gold Plated?

No, as of now, the gold plated variant is not available.