Has anyone figured out the vague areas that the different colors of cards, and the different types of symbols represent? Here's my best guess:
Bulb: Abstract Knowledge
Leaf: Environmental Knowledge? (antithetical to Red, which has no leaves)
Castle: Pre-gunpowder military
Factory: Post-gunpowder production
Clock: ??? Something related to knowledge, speed, and/or precision, and antithetical to Yellow (which has no Clocks).
Castle: Ancient/Medieval Military/Defense
Coin: Economic Strength/Wealth/Government
Factory: Industrial Production/Renaissance+ Era Military
Clock: Modern Technology/Modern Military ?
I'm glad I found this post. I was just about to ask the same question !
While learning the cards, I notcied that some cards had Dogmas which affected cards of specific colors, and was curious what the colors meant.
This post sheds some light on the "meanings" behind the colors.