Replace Feature Not Working As Intended, How to Fix?

Hello Forum, I was going about the use of the replace feature for colors, for animation purposes.

Only to find out that the replace feature only works well with solid colors, at least in my case.

I would find a solid color and try to replace it with a linear gradient color only to not have the correct intended effects.

However, the bucket fill works as intended, but cannot afford to replace every frame, and animation.

Looking for a fix work as the intended bucket fill.

Example shown below: