Portuguese infantry in the Napoleonic Wars did not carry a ‘national flag’. They carried a King’s Color and a Regimental Color. The King’s Color was the multi-colored design shown on the left in this picture. It was the same for all regiments. The Regimental Color had a solid colored field, and is shown on the right in this picture. The field of the Regimental Color was the same as that regiment’s facing color. (Hmm, actually not in this picture. That’s not what I expected to see.) These flags are shown in more detail on the Warflags site that I linked earlier.
You'll shoot your eye out, kid!