How to make a colorshift effect?

https://i.imgur.com/dTiXRIB.gif

Is there a tool that allows me to do a colorshift effect like in this gif?

The effect where the cape goes from black to red constantly in a fluid way.
I tried searching online, but I only find how to make glow effects, or how to shade light, not an effect like in the gif above.

I use a script to create a gradient that spans all frames:

Then I use a script to multiply the alpha of two layers, which shapes the blocks of color:

This is the result:

alucardBackDash

Obviously, were this more than a quick demo, I’d want to isolate the cape’s inner lining to its own layer. If I wanted the red pulsing to be more frequent, I’d add more red and black stops to the gradient.

[Edit: For more nuance, where the shading on the original cape is reflected in the red tint, I’d use a custom blend instead of a layer mask:

alucardBackDash2

]

Alucard sprite sheet source: The Spriters Resource - Full Sheet View - Castlevania: Symphony of the Night - Alucard

The sotn decomp project might give you a more exact idea of how the effect was created for this case, depending on if the community has gotten to that part of the code.