I use Prevail Protective Underwear which are white and look very similar to underpants. The only problem with them is the tops are quite high so you have to roll them down or have them sticking out of the top of your pants - see http://www.firstquality.com/products/retail/prevail/undwr.html for more information. There is another problem though with these when you need to change you need to remove your pants to put a new one on. I've found there is only enough room to do this in a disabled toilet, I hate using the disabled toilets to change though as you have to walk around trying to find someone with a key for hours. Most of the times I use the normal toilets which is a bit more tricky to change underwear.