i bought a white fly more as there were no colours available at the time. I would have liked a coloured one, I’ve seen the coloured tops for sale. Is it easy to change and would it void the warrenty?

You can put a skin on the spark no need to replace the top.

https://www.pgy-tech.com/skin-series-for-spark

You can put a skin on the spark no need to replace the top.

https://www.pgy-tech.com/skin-series-for-spark

I would not recommend you replace it on your own. You can ask the local service center for help. Here is the link: http://www.dji.com/service/repair/centers.