I downloaded a couple templates from templates.marketo.com and am trying to customize the background colors in the header, etc. but can't seem to do so.
Is there a way to customize these features? and is there a limit to what you can change in these templates (specifically the email and landing page templates).
You should be able to if you extract the HTML and then edit it directly. Then create a new template and copy the html back.
I was also informed to go into the Design Studio and select the template from there. Then edit the HTML in the HTML Source tab. This way when I clone the templates later on they will all show up with the customization I made to the original.
Like Josh Hill said... you can customize them to your heart's content.
I typically save the HTML of all my landing page & email templates offline, both for archiving and also for editing... Dreamweaver is a much better platform for editing, and I find the split view between code & design really speeds things up. Our most-used emails came from the Marketo Templates site, so I can vouch for their flexibility with any brand guidelines.