This is being written for the Xbox 360 build of Halo 3, but can easily be done on MCC as well.
Giving Brutes non-blue armor
If you have spent a short amount of time on this website or on the HaloMods subreddit/discord, you may have had the question of "how do I make brutes have different armor colors, like other enemies?" In your search, you will have probably come across this guide (https://pastebin.com/Bqu7CrtS) that explains one way to fix this issue. That guide explains that the Brute armor colors found in the Biped ARE being used in-game, but that the shader applied to the armor is essentially overriding the color with a blue-colored overlay; the solution goes into detail of how to edit the shader so that this is no longer a problem. If you have PC modding tools, you may have also seen this (https://www.nexusmods.com/halothemasterchiefcollection/mods/1476) post on Nexus on how to make/use improved Brute shaders. This is by far the best solution, in terms of quality, but it also cannot be used on the 360 (or on the PC without the modding tools installed).
This will work on the 360 and on MCC, all you need is Assembly. You will be making 1 new tag and editing the contents of 1 existing one. For best results, repeat this process for each map.
tl;dr
1. Duplicate the Cheiftain_Armor shader tag under rmsh (name it whatever you want)
2a. Go to your new tag and open it.
2b. Under Parameters, change the bitmaps for:
0-17(18) minor_major_armorwork
2-17(18) minor_major_armorwork_cc
3-17(18) minor_major_armorwork_bump
2c. Under Postprocess/Textures, change the bitmaps for:
0-5(6) minor_major_armorwork
3-5(6) minor_major_bump
2d. Save the tag.
3a. Open the Brute render model (under 'mode', name is just 'Brute')
3b. Under Materials, change the shader for:
3-15(16) [YOURSHADERNAME]
3c. Save the Brute tag.
4. Go test it out!
Final thoughts
I hope that folks find this little tutorial helpful. Obviously with MCC on PC, there are better ways to do it and have more control over how the shader ends up looking. I'm not too familiar with biped colors and the like, but I hope that this gives you a jumping off point to recolor and such however you want. You may still have to mess around with the float constants to get your desired results (the 'contribution' floats especially can add tints of environmental color to the metal when you may not want it, for example). Enjoy!
Pictures (biped colors are default values, Xbox 360)