The reason most 00 flours will not brown as easily as American flours is because they are less enzymatic (due to the ash content), and have no malt, as Tom pointed out. In order to have a 00 brown more easily you will need to have a dough that is more developed in terms of fermentation by adding more yeast, adjusting hydration, fermenting longer, or adding sugar or malt.
And from your pictures, your solution of adding sugar and lowering the hydration worked well.
John