fog lamps are actually concentrated lights. In front they are projected on road, not on the horizon. Yellow lights penetrate into fog smoke and distinct shaded areas from fogged ones. If you apply high beam in fog you loose visibility rather than gaining some, because white light and fog blend together and amplify the smoke.
in the rear, fog lights are more concentrated than brake lights, and even provide better visibility than hazard lights. But rear fog lamps come as standard in European cars only.
but aftermarket fog lamps with no projection & concentrated design, are actually all show no go stuff. but yellow lamps will still work, as per their property of not blending with smoke.