Find the style config file in /usr/local/share/fluxbox/styles/ then you'll need to edit one of the following lines:
Code:
menu.title: flat crossdiagonal gradient
menu.title.color: rgb:c/6/6
menu.title.colorTo: rgb:6/3/3
menu.title.textColor: white
menu.title.font: lucidasans-10
menu.title.justify: right
menu.frame: flat crossdiagonal gradient
menu.frame.color: grey40
menu.frame.colorTo: grey20
menu.frame.textColor: grey85
menu.frame.disableColor: rgb:4/2/2
menu.frame.font: lucidasans-10
menu.frame.justify: center
menu.bullet.position: right
menu.bullet: triangle
menu.hilite: flat crossdiagonal gradient
menu.hilite.color: rgb:c/6/6
menu.hilite.colorTo: rgb:6/3/3
menu.hilite.textColor: white