Editing the Numerique homepage gradient color:

Click on "Edit with Elementor":

Locate the first section's Style tab > Background:

You can check this article for more details: https://elementor.com/help/gradient-background/



Editing the Numerique inner pages gradient color 


Click on the "Solution Single" Single Page template (the template name may be different):

Open the Single Page template settings > Style tab > Background Type:

Check this article for more details https://elementor.com/help/page-settings/