Variable/gradient fill under curve

[pika]

Is it possible to fill an area under a curve where the color of the fill is based on the value of the curve at each sample?  It appears that the fill will always be constant, but I'd like it to be a function of the curve values.

Here's an example of what I'd like to achieve:  https://www.transformsw.com/wp-content/uploads/2013/04/workflow-welllog.jpg 

Any help is appreciated.