After MUCH playing around, I think I figured out the issue, the only problem is, I don't know what caused it:
The "Value" slider in the Colors window was dim. The box where the green arrow normally is was solid gray. As soon as I clicked on the box, the arrow appeared and everything was fine for that prop.
Any idea how that happened and how I can fix it without having to go into each sequence and do that to every single effect on groups, models, strings and nodes?