what is the diference between red onions and white onions ?
Taste? or its only the color ??

If you're cooking with onions, I'd go with a yellow onion. Red onions are less strong and more sweet, and are much better when using the onion raw (like in a salad or something). Yellow onions will give you the biggest flavor, white onions are a little more mild also.

the red ones are not less strong. they have more taste
however they also taste a little different.
i prefer red ones over yellow ones in general if the meal depends on the onion. if not you can also use yellows

Less strong in terms of that pungent onion-ey smell that makes you cry when you work with them.

I've cut 100's of pounds of onions by now and I'd have to disagree. they'll both make you cry

red ones are sweeter. i usually don't cook them because they already have a good taste. go good on salads and sandwhiches.
white and yellow are stronger flavor so i prefer to cook these before eating.

Red is sweet.
Goes better raw.
Yellow is like flavor full more used for cooking with hot temps