wave warp effect not working

Hi,

I drew some clouds first. then  a path.. Later I make the clouds follow the path. Suddenly I want to add a Rainbow which will emerge along with the cloud.  I draw the Rainbow, and used track matt for it. But am not quite happy with the result. Its not smooth. so far I have doine this with all the things I have learnt in past week. So I lack knowledge obviously.

Is there any way I can Make the rainbow path hidden and later it will emerge with the cloud as the cloud starts moveing?

Like we make the cloud follow the path at first?

I want some pro advice on it.

Thank you.