Step 1

Create new document, insert some text to layer and name it with text 

Step 2 

Add new layer and fill with color,name it with bg 

Step 3 

Add new layer, create circle shape and fill in with gradient color 

Step 4

Set color like this:

Step 5

Replace text layer to the top of layer

Step 6

Select text layer and press on right mouse, choose Mask 

Step 7

 Select the circle layer,make motion of it

layer should be perform like this :

Step 8

Test movie with Ctrl+Enter

Done!