Pattern fill to vector shape?

Here's what worked for me: 

Object > Expand

Object > Flatten Transparency

Object (or right click shape) > Ungroup

Object (or right click shape) > Release clipping mask

Select only the stripes (not the clipping mask outline) then Object > Compound Path > Make (or command+8) 

Then select both the stripes and the clipping mask and use Pathfinder > Intersect

Now the shape is a vector you can fill with any colour.

A lot of steps but definitely better than drawing all the stripes by hand!