How to determine the percentage of translucency and color when overlaying white?

Question

Adobe Photoshop

Good day everyone.
Tell me how you can determine the percentage of translucency and color (iPhone color # 61686B on a translucent layer) when applying a translucent layer to white?

Answer 1

I do like this:

1. I find a hundred percent known light color in the picture.
   
2. I put color on it on the eye so that it looks like what is in the picture.
   
3. Then I manually select the exact shade of the superimposed color from the color palette.