Object colour change when adding a layer

Hi Miles, 

I'm happy to pop in and assist you further with your questions! 

Have you checked the Design tab to see what colors are included?

Here is what I see when I pull this up within your file:

I selected the DESIGN tab (red arrow). I'm highlighting the current design properties (underlined in yellow on the lefthand side of the screen) and pointing to the color palette with the purple arrow on the top right. 

Attached you'll find a modified .story file where I changed the project colors from pink to purple for you. I did this by selecting the Create New Theme Colors button.

From there, you can go through and modify each individual text, accent, and custom color, so it brings your vision to life!  

I do hope this helps! Please let me know if you have any other questions.