As mentioned above, hovering the cursor over the Grain Type heading on the Mash Acidification page should pop up a comment box that helps explain how malts are typically classified.
The typical quandary in selecting grain type usually centers on Base or Crystal. Fortunately, there isn't a big difference in the acidity vs color for either of those classes of malt. In addition, most recipes don't include more than about 20% crystal malt content and the majority of most grists is base malt.
Remember, that Roast Malts will always have a color rating of greater than 180L. While there are toasty malts that might seem to be roasty, unless their color is over 180L, they have not been pyrolyzed to the degree necessary to move their acidity into the 'Roast' category.
