One can easily reverse engineer this image. the transparency grid of a screen capture makes it slightly harder to do but still not a big problem. Alpha blending is:

    total_Alpha = top_alpha + bottom_alpha(1-top_alpha)

so in this case we get:

    0.95 = x + .88 (1-x) =>
    0.95 = x + .88 - .88x =>
    0.95-0.88 = 0.12x =>
    x = 0.07/0.12 ≈ .58

Now this is correct if you measured correctly but i have some doubts about that but since you show it on a transparency grid i wont bother to verify my calculation.

    total_RGB = (top_rgb*top_alpha + bottom_rgb*bottom_alpha(1-top_alpha))/total_alpha

Where its convenient to calculate with float colors so colorshannel/255 in your case. I will leave this calculation for you to do.