How easy is it to replicate this effect?

Hey all,

I'm currently designing a new mock-up label for an air freshener and seem to be struggling to replicate an effect. Just wondered how easy it would be to re-create the following effect. 

I'm looking to create a colour swoosh effect in the dark green area similar to the blue one below that would follow the curve direction (not as complex) and help to emphasise flow but haven't had much luck yet. Is the below effect created using transparencies/arc's and fountain fills?

Thanks in advance!