AFAIK, no assets are covered by the license (models, sounds, textures, etc). You might be free to use the colormap. Read the 'legal status' section on this page regarding quake 1. It could be a similar deal with quake 2 - you'll have to do some digging. 

Open source AAA game communities find it insulting when some of their members want to create a commercial product out of the open sourced game that originated their community. This is why posts about projects like yours gets replies such as the #1. For some reason it's a kind of ethical or moral code that tends to exist in such communities.

Anyway, does the Quake 2 OpenGL renderer actually use the colormap.pcx data? Maybe you can replace it with a different 8-bit color pcx image with the same dimensions. 

Colormap.pcx is used by the GL renderer, but only in that it's the source for the palette. Beyond that it's software only.

You could in theory provide any PCX file and read the palette from that instead. 

Thank you for the responses. We aren't commercial product and we plan to release all assets to open source. Our only question was related to Quake 2 assets. Think of it as mod re-using Quake 2 assets, but also changing the client. We don't plan to make our assets private nor sell them. All of our work is for cause of open source. I'm sorry I didn't mention that in my OP.

The only issue we have is with the game assets themselves, I believe we could re-use assets if player owns the base game. Effectively being a mod that also modifies executables. 

P.S. We use colormap.pcx at least during development to make our textures use the Q2's palette. It's probably the worst example I could mention because the end-user doesn't require it. However, I did mention sound files, which we'd like to reuse in some way. We don't really have sound equipment capable of recording those, nor the budget to cover that. I personally only came with 4+ years of C development experience and my friend works on art assets, so we slowly progress towards our goals. We've chosen Quake 2 engine (Yamagi Quake 2) because it's the closest to what we need to our vision we have. I personally fancy C development and the productivity is rather high lately. We've had attempts at Unity, Torque3D, or even tried to develop our own game engine (which turned into its own project as an engine replacement for Mafia: The City of Lost Heaven), but Quake 2 was the closest match for us. There are some quirks in asset creation pipeline, but we've sorted out how to develop assets effectively already. I really love the community and always had the dream of creating a retro RPG styled game in Quake 2 codebase. 

About the sound files, there's a ton of royalty free sound effects on the internet. Just search on google for "download free sound effects" and you'll find replacements for every occasion that you may need ;) 

That's fair, I believe that is all I needed to ask about then. Thanks. 

include any assets. And by requiring Q2 you are limiting your audience.