Thanks - regarding eMail-header, now I found it...
Using hex-code: understood. That was kind of a placeholder anyway...
Drag&Drop Editor: I agree as well. Just wanted to show the planned mails not like a typical newsletter, thats why I was using plain text only, like in a regular eMail... 😉
Regarding changing the colors: I tried this (with span as well):
<div style="color: red!important;">{unsubscribe}your text{/unsubscribe}</div>
In the preview, it shows up in red. But when I am sending out a test mail, it still shows the ugly blue in my mailbox.