How to match a color at 100% opacity with color at 50% opacity?

No vacuum, of course. I would never claim that. But considering the numerous mediocre PDF viewers that are not able to display even "simple" transparent objects and interactions correctly, I'm certainly a bit out of the game in this respect.

I will post a picture as soon as I am a full-time shepherd.

Good point, Ton.

On the other hand I'm not quite sure if I should really be responsible for the inability of countless PDF viewers to accurately display proper PDF constructs.

If that may be the case one day, I will immediately convert myself into a shepherd.

Perhaps, Ton, we may reach an agreement and claim that the woody thing is possible and impossible at the same time. Depending on the point of view and concept.

Nonetheless, it may be pretty interesting if you could provide a sample file that may prove that it is impossible in some situations.

The light green rectangles (in file woody_impossible.pdf) have slightly different colour values. That won't work accurately, of course.

Left rectangle: H=59,66 – S=98,32 – B=86,95

Right rectangle: H=59,55 – S=100 – B=86,96

Here is another sample file:

https://drive.google.com/file/d/1D9nJldI_-EZ77Q4NlarY2VUVuDnY9rOM/view?usp=sharing

Doesn't that work for you, Ton? Or are we still talking at cross-purposes?

No, of course it is possible, Ton.

We are probably talking about different things or thoughts.

I'm not quite sure what you mean, Ton. Can you elaborate?

Or in other words: What behaviour (interactions) do you expect in the woody.ai and the woody_possible.ai files?

"Trying to adjust the 50% to mimic the original 100% color is a moving target and impossible with saturated colors."

Possibly it's possible, Ton.

https://drive.google.com/file/d/123QDl7-e-u95BctBcfdB3n-kEi5S7_CF/view?usp=sharing

Marco Emilio,

Actually, I came to think that it will sometimes be possible to at least get close for certain pale to mid tone colours:

You can try this, starting with the desired 100% opacity colour:

1) Move a copy of the path with the colour and set the Opacity as desired (as you have in the screenshot/image);

2) Switch to CMYK colours, but only in the Color palette; I am/have been assuming that you are working in RGB;

3) Select the original and (albeit only temporarily) clear the insignificant CMYK values (it can be one of the CMY and K) and change the significant ones to the nearest integer values (just to remember more easily), then insert higher values in the lower opacity copy and adjust the relevant C/M/Y values to get the best possible match;

4) Optionally, you may consider a certain adjustment of the original full opacity colour;

5) Switch back to RGB to get rid of the ugly colour values;

6) Optionally, you may fine tune the colours in RGB.

You can see a sample done hurriedly (without fine tuning) that way below; the dark one is the pale one at 100%.

Edit: My earlier (mis)conclusion was based on failed attempts with HSB, in line with the suggestion by Ton (which I saw when finally finishing this post); and then realized that the greyscale only way pointed at the similar CMYK way, both opposite to RGB.

I am not sure if I understand what you are asking, but if you want a 100% color non transparent color that looks like the 50% transparent color, just select it and choose Object > Flaten Transparency...