Remember: for metallic colors, you want to pick the lowlight where the color appears darker, but not darkest. This is because the darkest parts of the paint are where the shadows are the strongest, which influences how the paint appears. For the highlight, you want to pick where the color appears the brightest and most vivid. With darker colors like this, you need to manually stray away from the values that the color picker gives you, especially for the brightness. If you have a lowlight with a low brightness (say, 0.33 or lower), a highlight with a hight brightness (say, 0.75 or higher) will really change the way the color appears in-game. For this reason, you need to lower the brightness of the highlight so that it is not too flashy and gives the proper effect.
Using your reference image (because it's a great one), I made a version of this color for my own spreadsheet, and to use as an example. I used your image and I highlighted areas that I picked for the lowlight and highlight values:
View attachment 1158595
From there, I picked the values and produced the color in-game:
View attachment 1158596
Another time when you need to change the values the color picker gives you is when the hue is off. I find this happens the most with orange colors and bluish-green colors like this one, although it can happen with other types of colors. In general, when I am adjusting the values, I go in increments of 0.05 on the sliders, and then 0.01 when I am fine-tuning. This is so that I can pinpoint the exact values that will produce the closest replica.
Another thing I feel like I should say is that every screen is calibrated slightly differently, so every device will show colors slightly differently. I always try to get the color as close as I can on my TV because that's what projects the game. I know at that point that the color is accurate and that, even though other devices will show it slightly differently, it is still accurate where it needs to be.
I hope this helps. These are things I had to figure out on my own as I continued to do this a few years ago; no one gave me much advice. It is nice that we are doing this now, so that it can be documented for people who want to get into this.