computation algorithm of color with opacity

[Vincent Torri]

Hello

in a program of my own, i would like to compute transparent colors and I find that the colors computed with the area chart are quite beautiful

i tried to see if, using HSV, I could find the algo, H is not modified, but just multiplying S by the opacity is not sufficient, V is also changed a bit. And I can't find how V is changed

does someone  know what the algorithm is, please ?

thank you

Vincent Torri