As defined by FEDERAL DOT LAW,
And adopted by most state laws,
Your 'Fog' lights must NOT operate when high beams are on,
Must be AMBER,
And must be directed at the ground directly in front of the vehicle.
You can wire them to automatically disconnect when you hit the high beams,
And you can have them on when no headlights are turned on.
Now, if you are talking about driving lights,
Again, the law is VERY specific,
One pair of PRIMARY driving lights (LOW BEAMS), White in color.
One pair of SECONDARY lights (HIGH BEAMS), White in color.
One Pair of 'Special Purpose' lights, Amber in color (FOG LIGHTS) are allowed.
There are also specific distances from the ground that forward facing lights can be...
Minimum and Maximum, and I can tell you, they don't allow roll bar mounted lights!
Most under bumper lights are too low and 'Illegal'...
Even though it's not enforced most places, if you travel, sooner or later you WILL find someplace that will fine you!
Like Las Vegas crammed three tickets up our butts two years ago for having forward facing white lights other than 'Primary & Secondary (high and low beams),
'Rock Lights' in the wheel wells,
And rear facing lights on the roll bar...
And it was at a 4 wheel drive show on the road in front of our hotel!
The laws are enforced VERY spotty though,
Some places let you get away with forward facing White lights, like driving or off road lights,
Other places require you cover them up when on the highway.
Just turning them off isn't enough...
(ask me how much it cost me to learn that in California...
Let me know what lights you plan to run, and how you want them to work, and I can likely throw you a wiring diagram that will fit your application...