How to use custom prefix color?

I do not understand how to use the "Custom Prefix Color" option in Formatting Options.

Could someone please provide a way to use this? I have tried inputting "255, 234, 141" into the input box, to get a custom colour, but minecraft crashes straight away and i have to open the config.json for 5zig and manually change the value back to nothing before minecraft will relaunch. If this is not implemented or if nobody knows how to explain its use, maybe an rgb slider could be implemented to change this?

TL;DR: How can I get a custom rgb using Custom Prefix Color

Look at the formatting options UI code where the custom prefix color input is handled. Check how the input is parsed and validated, likely in a class related to configuration or GUI. The crash suggests improper handling of the RGB string; examine the error logs from Minecraft to identify the exact exception. Test with valid RGB formats to ensure the fix works without crashing.

Written by the indexing model from the issue text.