The things you need to know to learn about LWO is that if you breed a LWO+ stallion to a LWO+ mare, and the resulting foal gets a copy of the gene from each parent (making it in effect, homozygous for the LWO gene), the foal WILL die due to an incomplete intestine. There is a 25% chance of this happening. You also have a 50% chance the resulting foal will carry the LWO gene, but will not be lethal, and a 25% chance the foal will not carry the LWO gene.
If a LWO foal is something you don't wish to have happen, (as most responsible breeders wouldn't) then you need to test your horses to ensure that both the mare and stallion do not both carry the gene. It is 100% SAFE to breed a LWO+ to a non-LWO+ horse without worries of a lethal white foal resulting.
As for pattern, you cannot tell just by looking in all cases, if a horse carries LWO, and that is why it is most important to test. Something as simple as a blue eye, a sock, a star or a blaze can mean the horse is LWO+. Just like any other pinto pattern, even a minimally marked horse can throw a loud marked foal, so there is no need to double up on the LWO+ to try to get "more color".