How to apply a filter that changes section border

Hi!!
I have a loop template that I am applying to a certain page to show a particular custom post type as a grid.
I am able to show different custom type fields with this template using the dynamic content option and that is great.
The template has all the content is one big section. This section has a nice border.
What I want is to change the border color according to the value on one of the custom type fields. That particular field can have nine values, and I have a color for each value.
I think that I could get this done by coding a filter in my functions.php file. But I do not know what hook to use; and I would not know how to pass on the custom post object data to the filter function so that the function uses that data in the logic and returns the section content with the border color changed.
Any ideas?