Firstly, can I colour it using paste colours like shop bought fondant?

and secondly, does it roll out like shop bought fondant?

Thanks for any advice

Yes to both!

yes to both. if you want to make a batch all one color you can add the gel color to the melted marshmallows before adding the PS, otherwise you can color small batches when the MMF is done.

brilliant, thank-you. I will have a play over the weekend & use it for my record decks if it turns out ok