Customising colours for SharePoint Online's 'change the look' feature?

[toby.mcdaid]

I have a set of colours which our business uses for design projects. For SharePoint Online I need to be able to set each site to match these colours which I have hex values for. 

When I select SharePoint Online's 'change the look' option, the only colours I can pick from are the default colour pallets that Microsoft have given you. I can't customise the colours to my specific needs, not through the default interface anyway. 

Anyone know how you can do this?

Thanks

[#2]

You can create custom themes for your SPO sites and deploy them using PowerShell. You can find information about the process here: https://laurakokkarinen.com/how-to-create-a-multicolored-theme-for-a-modern-sharepoint-online-site/