Permission Issues Uploading Custom Color Scheme in SharePoint Online

[SamG89]

I am struggling to upload a custom color scheme to a sharepoint online site. 

I am missing all of the customization items from the web designer galleries section in site settings, but have navigated to /_catalogs/theme/15/.

When I upload from within the /15/ folder, I get the error 'The documents cannot be uploaded because different permissions are needed. Request the necessary permissions.'

All my internet searches point to this being due to not having custom scripting enabled at a tenant level, but this is not the case. In fact, a separate site under the same tenant built by my predecessor uses a custom color scheme. 

Is there anything else that could cause me to not have permission to upload a color scheme and have items missing from my web designer gallery? I have owner permissions on the site, which is a communication hub site. 

Thanks

[#2]

@SamG89 

Hi, are you a Site Collection Administrator for this site?

[#3]

Hi @PeterRising ,

I'm a global admin on Office 365, so per my understanding I should have all Sharepoint permissions. Is that not correct?

[#4]

@SamG89 

No not at all.  GA permissions are unrelated to Site Collection rights.  From the SharePoint Admin Center, highlight the site in question and go to Permissions > Manage Admins as shown below.

Make sure your account is included here.

[#5]

@PeterRising 

I don't have a 'manage admins' option, just 'manage group owners' and 'manage additional owners'.

I've made sure I'm in both lists, but still no web designer gallery permissions.

[#6]

@SamG89 

OK, try using the SharePoint Online Management Shell and run the following commands, just to double check the customization settings for this site.

Connect-SPOService -Url https://tenantname-admin.sharepoint.com

Set-SPOSite -Identity https://tenantname.sharepoint.com/sites/sitename -DenyAddAndCustomizePages $false

[#7]

Thanks for the suggestion @PeterRising - don't have the management shell installed on my computer at home because I'm a Mac user. I'll try this on. my windows machine when I'm in the office tomorrow. 

[#8]

@SamG89 

Ha I'm also a Mac user first and foremost.  Let me know how you get on.  Hope it works for you.