plotting XY curve with diff

I have a 100 data sets that I want to plot XY data on the same plot.

For one data set the XY curve looks similar to what is shown below.

I want to plot the the upward curve one color and the downward curve another color. These happen at different times in each data set.

how do I identify the changing point in each XY curve and plot it all in one graph?

I tried using Y gradient but wanted to see if there are suggestions.

Thanks.