Changing color gradient of scatter plot using ColorMix1

[Sellls]

Hi,

I'm trying to get a different color gradient on my scatter plot using the custom color expression.

Am trying to achieve the same effect as the attached picture but with a green gradient instead of the default orange to dark red.  I basically want the newest data points to be darker in color and the oldest to be lighter in color.

I've tried to use the following code but it doesnt work. [Month_out] is the dimension in this case, and so is the measure.

Colormix1( (([Month_out]-$(=min([Month_out]))),[Month_out])/(($(=max([Month_out]))-$(=min([Month_out]))),[Month_out]),Green(),Lightgreen())

Wondering what I'm doing wrong , as the plot just turns out entirely grey?

Thank you!