When I have colors on a graph with 2 variables corresponding to different values, how do I make a legend from it?

I am making a graph where there is a variable on the x-axis and one on the y-axis. Both variables have 3 levels and for every combination of the two, a certain parameter has a particular value.

Now depending on what the value is, I have marked that spot on the graph with a certain color. That is what I want to show in the legend - A certain color for a certain range. The graph has been attached for reference.

Any help would be appreciated. Thank you!

Answer 1

[magate]

Plot NaN data for the legend.

See this answer here .