It’s not really the Jazzy Forms related question. You can learn about CSS border-color property (and much more) at w3schools.com (http://www.w3schools.com/cssref/pr_border-color.asp). Anyhow, if you are talking about input field border herе is an example:
.jzzf_form input[type=”text”] {border: solid 2px #FFF000;}
Cheers!
I’m glad I was able to help. Do not hesitate to ask questions. It takes a while to learn about CSS, WP, JazzyForms etc. I’m still struggling with my current project to make a “perfect” appartment-renovation cost calculator.
Have a good one!