It is often not explained that there are many different recipes for ragù in Italy for two reasons.
There are very different ragù recipes in the different regions -- this is fairly normal as Italian cooking is regional. I assume that you mean the ragù with minced beef common in Italy's "food valley" in Emilia, and not the Neapolitan recipe with meat cubes.
Even within a region, there are many variations of some recipes, especially recipes with many ingredients, down to the town or even family level. Ragù di Carne is one of those recipes.
That said, what I can give you is some general guidance. You can use either white or red wine for it as long as it's dry. It's more important to understand what else is in your recipe.
If your recipe has dried porcini in it or salamella sausage, go with white wine as you already have strong flavors.
If your recipe only has beef mince, perhaps red wine will give it more flavor.
If you are adding tomato or tomato paste, the ragu's color will be brown/red no matter what wine you choose. However, if you don't use it, then red wine will likely give it a better color.
Finally, try to be local: a wine from Emilia is probably better than one from Sicily.
In conclusion: there is no correct answer to your question but remember that Ragù, like all dishes with a layering of flavors, requires careful balancing, so experiment and understand which is best for your recipe. Perhaps you can create your own family variation of Ragù!