Stocks

Start with cold water and don't let it boil. Bring to a boil and return to a light simmer. You could also try blanching the bones ahead to coagulate the proteins. I haven't done this, but it should help. If it is still too cloudy, follow peirino's advice. Also, I like to use large coffee filters inside a sieve for straining to get the smallest particles out.

It's the proteins coming out of whatever "white" thing you are making stock from. It's inevitable. To be clear like a consomme you'll need to skim the top and ultimately strain it. You can also use a "raft" of egg whites to collect some of that protein material after it surfaces. You didn't specify what kink of "white" you are asking about. That would be useful to know.