This is chromatic aberration, often seen as purple or green fringing along high-contrast edges. It happens because a lens does not focus all wavelengths of light to exactly the same point; different colors bend slightly differently through the glass.

Yes, it comes from the lens design and is an intrinsic optical limitation to some degree, even on good lenses. It tends to be more noticeable in high-contrast scenes and can be stronger when shooting wide open.

To reduce it, photographers typically:

• stop the lens down a bit instead of using it wide open
• avoid extreme high-contrast edges when possible
• correct it in post-processing using chromatic aberration/fringing removal tools
• choose lenses that control CA better when this is a priority

So your lens is not necessarily bad; this is a common optical issue, just more visible in some situations than others.