The legionaries in the first books (Asterix the Gaul, Asterix and The Golden Sickle, Asterix and the Goths, Asterix The Gladiator and Asterix and The Banquet) bare a great difference to the legionaries in the later book. The colour of the armor, toga, shields switches form red, green (dark), yellow and even purple and violet. After the sixth album Asterix and Cleopatra they all wear green toga's metal colored armor and blue shield. Here is how their cloths change during the course of time.
Asterix the Gaul[]
Toga (cloth under armor) - Purple, Yellow, Violet, White
Armor: Purple, Light Purple, Red
Shield: Yellow, Brown, Purple
Asterix and The Golden Sickle[]
Toga: Blue, Green, Yellow, Red
Armor: Brown (Rusty), Blue to Grey
Shield: Green, Blue, Red
Asterix and the Goths[]
Toga: Red, White, Purple, Blue (dark)
Armor: Golden to Yellow, White (due to printing)
Shield: Golden to Yellow
Asterix the Gladiator[]
Toga: Red, Green, Blue, Purple, Blue (dark)
Armor: Golden to Yellow
Shield: Blue
Asterix and the Banquet[]
Toga: Green, Red
Armor: Metal - Grey
Shield: Blue, Red
Asterix and Cleopatra[]
Toga: Green
Armor: Metal - Grey
Shield: Blue