Different color for error's and warning's

Hi @ipadawan.

That information is for Arduino IDE 1.x. Arduino IDE 2.x has a completely different theme system, so any information you find about Arduino IDE 1.x themes is not relevant.

A community member shared some information about using 3rd party themes, and creating custom themes for Arduino IDE 2.x here:

You should install themes under a folder named plugins.

It should definitely work if you follow the instructions provided in the post I linked above. If you follow those and still encounter a problem, provide a detailed description of what you did and what didn't work in a reply here on this forum topic and we'll try to help with that.

Please note that Arduino IDE 2.x does not support Arduino IDE 1.x themes, so if you installed an Arduino IDE 1.x theme, then it is normal and expected that Arduino IDE 2.x did not recognize it.