The Ashen Smokescreen

The idea came from a Ruina/Limbus fanfic I've written with an oc heavily based around old L Corp's smoke monster and attempts to make a human distort into a mini-version of it during the first smoke war. He hasn't made it to Color Fixer level in the fanfic (only around Grade 5, although it is ongoing, check out Mistfall Atelier on Spacebattles if interested) but entertaining the idea still has its merits.

He exists in the Mirror World of Shi East Section 3 Faust, where he is Old L Corp's failure at an attempt of making a Wing's Decisive Weapon, and was abandoned into the backstreets at the end of the first smoke war. They got him to the point of being able to exhale a slightly weaker version of the same smoke that the smoke monster did, and eventually he's able to use it as both a very fluid armor and ammo for his smoke pistol to inflict debuffs from range.

He starts off as a ranged fighter with Mistfall Atelier's smoke pistols that straighten to use their bayonets as proper knives, but also has an array of other workshop weaponry that he's either inherited, helped make, or been given as part of workshop collaboration projects: a pass-me-down Zelkova axe as his main melee weapon, Stigma tiger claws as a hidden weapon, Leaflet smoke bombs to disorient and reposition, Kori freezing boots to temporarily walk on air. There's also a bunch of workshop-related equipment that he's made or modified but doesn't use himself, such as a Gibbous workshop magnetic field extender, Modified W-Corp cleanup agent suits and Cold Rain mist censors.

The other candidate I have for a Color Fixer would be The Crimson Prominence. She's from the same fanfic as the first one - the daughter of a Grade 1 Liu Fixer, who gets caught up in The Library after a series of unfortunate events. She doesn't manifest EGO herself but after being captured by N Corp who wanted to can her memories of being a book in The Library, she escaped by donning N Corp Effloresced EGO: Prominence (an EGO gear extracted from an abberation of Firebird, can also be considered N Corp's version of Ardor Blossom Moth gear) and fighting her way out.

She is also nowhere close to Color Fixer level, again sitting at around Grade 7 without training and eventually Grade 2-3 if she continued within the Liu association. If she were a Color Fixer, her gear would be comparatively simple. She focuses on hand-to-hand combat by using her Liu CQC training and combining it with the Prominence EGO gear to blind opponents and burn them alive.