Cosmo is like a galaxy but,another thing to say it's Saint's like an enegry thing,like how Seiya do Cosmo then,Pegasus Ryu Sei Ken (i watched Seiya vs Ikki) it's kinda powerful and make him kinda powerful (why do i have to say this 2 times) anyway,Cosmos have their own color.
Seiya's cosmo is blue.
Shiryu's cosmo is green.I don't have words to say about Omega characters.
Ikki,have Red Cosmo,he is very burn with a fire of Phoenix.
Gold Saint's cosmos are yellow.
To see Saint's cosmos click one of those image links.
Cosmo in baby:link
Cosmo of Ikki:link (Yes copying wikia's images but,it's better to forget it and look at images)
Seiya as toy with a Gold Pegasus Cosmo:link
I don't want to put villain's cosmo.
Cosmo without any characters:link
Tenma's cosmo:link
That's all i have to say,Cosmo is not only one color.