This page lists the enemy shield types that are vulnerable to different damage types. When I was playing recently, I noticed that a particular shielded enemy was resistant to Solar damage. Are enemy shields that are vulnerable to one type of damage resistant to another type of damage?
Colored shields are weak to elements with the same color. If you shoot an enemy with a blue shield with a rocket launcher that causes void damage, you will still hurt him, but not do bonus elemental damage.
Bonus damage is usually displayed in the same color as the element, when shooting an anemy with the same colored shield.