The Hue Saturation module might be suited to this task as it contains function curves and is fully animatable over time.
Looks like you would need to incorporate an Image Switch module to animate the Color Override over time but that is only available in Harmony.
Nice to see you figured something out and thank you for following up. Everything helps in understanding how the software works.
Lilly of Toon Boom describes using the Transparency module for animating an effect:
"Here I did a quick example of how to do the blending with transparency effect:
So I have a drawing that is just basically a rectangle filled with a colour. In this case, if I want to go to a night-time scene, I can make this colour a dark blue. If I wanted to change it to a sunset or something, then I would have the colour be a pink or orange colour.
Then you attach this rectangle layer to a transparency effect, and the transparency effect to a blending node. In effect now I’m using the rectangle as an overlay, like a film on top of everything that’s underneath it. I choose one of the Blending options, like Multiply.
Then, to animate from one colour to another, I animate the transparency. I will start out at 100% transparent, for no effect, and then I will animate it down to 50% transparency or so for full effect.
Of course the same effect can be done in Animate Pro, and the advantage there is that you can get more complex combinations of modules to get some neat effects.