The "lighter-hued regiments" were who?

"When the woods again began to pour forth the dark-hued masses of the enemy the youth felt serene self-confidence."

Well, if the darker-hued masses were the enemy; the lighter-hued regiments would have been Henry's Union regiments.

"They struck savagely and powerfully at each other for a period of minutes, and then the lighter-hued regiments faltered and drew back, leaving the dark-blue lines shouting. The youth could see the two flags shaking with laughter amid the smoke remnants."

I take it back; the lighter hued garments belong to the opposing army.