Thank you so much for your help!

Here are directions for Windows. You'll have to adapt them if you're using a Mac.:

In your main Opera GX profile, goto the URL opera://settings/side-profiles-settings and create a new profile with the color you want.

Then, launch the profile you want to modify, goto the URL opera://about in it and take note of its "profile" path. Then, close that profile.

Then, launch the new profile you created, goto the URL opera://about in it and take note its "profile" path. Then, close the profile.

Then, unpin the taskbar button for the profile you just created and for the profile you want to modify. Also delete their desktop shortcuts if they're present.

Then, in Windows Explorer (File Explorer), with "file extensions" and "hidden items" enabled under "View -> Show", browse to the new profile's profile folder and the profile folder for profile you want to modify.

Then, you want to do 2 things:

• Copy the "On the side.ico" file in the new profile folder and paste it into the profile folder for the profile you want to modify (choosing to replace the existing "On the side.ico" icon there). Don't worry if the color of the "On the side.ico" file doesn't update to the new color yet after the pasting.

• Open the "xxxxxxxx_sideprofile.json" file in each profile folder (where "xxxxxxxx" is a unique id for each profile) in a text editor like Notepad. You will see a color value in there. Replace the color value in the json file for the profile you want to modify with the color value from the json file in the new profile you created. Make sure to save your changes.

Then, open up the Windows Task Manager, switch to the "Processes" tab, select "Windows Explorer" and click "Restart Task" on the toolbar. This will update the "On the side.ico" file's color in the profile folder for the profile you modified.

Then, in your main Opera GX profile, goto the URL opera://settings/side-profiles-settings (or reload the page if you still have it open). There, you can remove that new profile you created just to get its icon and color. Then, for the profile you modified, click the 3 dots next to it and choose "Restore icons". Then, when Windows asks you if you want to pin the profile's icon to the taskbar, say yes. The color in the notification you get from Windows will probably still be the old color, but when the icon is placed on the taskbar, it'll have the modified color.