Hi Francois!
It sounds like you needed some help setting up templates for the question slides in your Storyline course. I'd be happy to get you some information on that!
A way to achieve this would be with the use of Slide Masters. Slide Masters are used to control the default themes, colors, fonts, text, and objects for slides throughout your course. They're big time-savers, letting you apply the same look and feel across multiple slides all at once.
Also, I found some related discussions where users shared steps for working with slide templates, and a guide on theme colors you might find useful.
Hope this helps! Please let me know if you have any more questions!