How to apply color gradient change on a fluid such as in the following figure? The method should be capable to apply to all frames in the animation automatically. Consider it as simulation of being heated gradually in some specified locations.
Update:
Here is our result based on accepted answer: using procedural texture. Indeed, the answer is perfect for this question.
One side comment is that as also mentioned in the answer, the color is not attached to the fluid so as you see the color of drop is changing as it moves. This could be our other question in other post.
