Edit area graph legend data

I have this area graph:

As you could see the legend refers to the x-axis data. How can I display the legend referring to the y-axis data (should be 104 data point not 50)?

Is there a better way to automatically change data colours? If I did not change Facecolor, different data are displayed with the same same colour.

Thank you

[KSSV]

Why you want to go for a legend? I think colorbar suits your need.

[Barbab]

Thank for your answrer.

I want my legend to look like this.

(I use different data for this graph)