Matter of opinion.
Personally, I liked Halo:CE’s and Halo 3’s bright aesthetics. They were dark where they had to be to set the mood, and bright where it counted.
I think your interpretation of the color palette in Halo is far off the mark. If light represent the known and familiar, and dark represents the new and unknown, then Halo:CE would be dark, and Halo 2 would have had a lighter color.
A better interpretation would probably be that a more colorful range of colors represents exploration, while a darker and more monotone range signifies survival. In Halo: CE, the brightest levels are the ones when we are exploring the titular ringworld, ending with “343 Guilty Spark”. And the level before (Assault on the Control Room) that was bright, but monochrome, an effective bridge between the lighthearted exploration of the first half of the game and the grim survival in the second half of the game.
The latter half of the game is dark and monochrome, when we are running from the Flood and attempting to disarm the gun aimed at the head of the universe. The exception is The Maw, the final level, where I presume the environment becomes brighter and somewhat more colorful to stir hope in the player as the crisis is quickly resolved.
The darkest Halo games (ODST and Reach) are a lot less subtle with their colors, and to be honest, I feel that they were trying too hard at times. Yes, the Noir-ish atmosphere of Halo 3: ODST was a great change of pace and well-executed in many places, but often the environment was so dark or washed out, it negatively impacted the player’s ability to play the game. Reach was better, but I’d love a return to the colorful vistas of Halo games past.
Darkness for the sake of darkness does not make a more mature or more serious story. Without light to contrast the darkness, or color to balance the grays, the color pallet can’t set the atmosphere. And if you feel differently, then I challenge you to show where the previous games were “EXTREMELY and unnecessarily bright.”
Anyhow, for the best analysis I’ve watched of tone and aesthetics in games, go here.
Death to ‘Real is Brown’!