If you are working on SharePoint modern pages and want to try new themes for your clients then get inspired from the samples given at SharePoint provisioning Site. Where you can see a bunch of themes provided by Microsoft.
If You like any theme just select it and Add it your tenant. To do that you must be SharePoint Admin.
Just go to https://provisioning.sharepointpnp.com/ or https://lookbook.microsoft.com/ and select the theme you like and Add.
These themes are available in git hub too at: https://github.com/SharePoint/sp-dev-provisioning-templates
Download design look book at: https://provisioning.sharepointpnp.com/assets/SharePoint_lookbook_2019.pdf
if you want to know how to add the new designs to your tenant. Please watch below video:
|.||Learn SharePoint with self paced training. please click image or go to course at: https://onetidbit1.teachable.com/p/sharepoint-basics|