You only claim the scale if the enemy matches the color of the scale.
Are you sure? I wanted to add this too, but I searched the manual and found nothing. Is this written somewhere? I recall this somehow, but perhaps I'm wrong.
The "Claiming Dragon Scales" paragraph says:
Claiming Dragon Scales
If a character kills an Enemy from a Dragon Card, in addition
to taking the Enemy as a trophy, he may claim the dragon
scale on his space and place it in his play area. Dragon scales
have two powerful effects:
• If a character encounters an Enemy or Draconic Lord, each
dragon scale the character has that matches his opponent
adds one point to his attack score.
• If a character is about to suffer a Draconic Lord’s Dragon
Rage (see “Dragon Rage” on page 15), he may discard one
of his dragon scales that matches the Draconic Lord to
cancel the Dragon Rage and not suffer any of the effects.
Characters may gain any number of dragon scales during
the game. Dragon scales are not considered Objects, Spells,
or Followers. Therefore, they cannot be ditched, stolen, sold,
or traded. If a character is killed, all of his dragon scales are
inherited by the player’s new character.