eval is a handy tool for making code snippets visible in the documentation, but it's not often needed while making projects with dialogizer. And it's probably working against you here.
This:
dd.open[deck] dd.say[yourcoolfield.value] dd.close[]
should be enough to play a scene written in a rich text field, with all of the formatting intact.
It's important that you point dd.say at the field's .value (which includes the rich text formatting) and not .text (which is plain text only)
If you strip it down and just put the above code snippet (with "yourcoolfield" renamed to be correct for your project) does it work?