Standard Header and Footer - HTML?..

Summary

Can you use HTML in the standard Header and Footer

Content

We are looking to make our TBE communications/emails a bit more colorful and more directly branded to our agency..

Has anyone been able to implement HTML into the Standard Header and Footer areas within the Organization > System and Email Settings?.. We put a test in, but it didn't work so are wondering if there is a button/switch we missed, if we need to have this done by Support, or if it is just not possible..

(We do know that we can change each individual communication from Plain Text to HTML however this doesn't seem like the most efficient route for any number of reasons..)