this is the css to customize the color , i already put purple in, you can change that to a specific color.
if you are using the bbpress-new ui plugin , i dont know if that will cause a conflict or not.
copy this css anywhere where you can put custom css
jetpack custom css module
custom css plugin
bbpress.css file
HEADER
#bbpress-forums li.bbp-header {
background: purple;
}
i also put the footer css just in case you want to edit that too.
FOOTER
#bbpress-forums li.bbp-header, #bbpress-forums li.bbp-footer {
background: purple;
border-top: 1px solid #EEE;
font-weight: bold;
padding: 8px;
text-align: center;
}
Links that might help
https://codex.bbpress.org/step-by-step-guide-to-setting-up-a-bbpress-forum-part-2/
https://codex.bbpress.org/bbpress-styling-crib/
https://codex.bbpress.org/step-by-step-guide-to-setting-up-a-bbpress-forum-part-3/