Chroma controls the primal elements. His abilities are altered depending on the element of his choosing, making him a very versatile warframe.
Chroma’s passive is Elemental Alignment. Chroma has one element he is attuned to which will alter the way some of his abilities function. When customizing Chroma’s appearance, changing his energy color will alter his chosen element. Only the four basic elements can be chosen, Heat, Cold, Electric and Toxin. There is an icon next to his energy color that indicates the current element.
Chroma’s second ability is Elemental Ward. Chroma emits an aura around him that has different effects based on his current element. Each different aura has an offensive and defensive component. The Heat aura will increase the health of Chroma and any nearby allies while dealing Heat damage per second to enemies, with a small chance to inflict a status effect, setting them on fire. The Cold aura increases the armor of Chroma and any nearby allies and creates an ice shield around them that reflects enemy ranged attacks back to them as Cold damage. This damage is amplified when reflected and has a chance to inflict a Cold status effect, causing enemies to slow down.
The Electric aura increases the shields of Chroma and any nearby allies. Any damage taken while this aura is active will be converted into electric discharges that strike enemies in range. The damage the enemies take is amplified and converted to Electric damage. Enemies can also suffer an Electric status effect, stunning them and chaining the damage to others nearby. These electric discharges have a minimum damage they will always inflict. Finally, the Toxin aura creates toxic fumes around Chroma and any nearby allies, increasing their reload speed and weapon holster rate. The fumes also have a chance to deal Toxin damage to nearby enemies, based on their maximum health, and will also inflict a Toxin status effect, poisoning them and dealing Toxin damage per second.
Ability Strength mods affect the damage of Spectral Scream, the damage and armor multiplier of Vex Amor and their maximum values and the health and continuous damage of Effigy. If also affects several components of Elemental Ward, namely the health bonus and damage of the Heat aura, the armor bonus, damage multiplier and status chance of the Cold aura, the shield bonus, damage multiplier and status chance of the Electric aura, and the damage chance of the Toxin aura. Ability Range mods affect the range of Spectral Scream, the aura radius of Elemental Ward and the range of the Electric aura’s discharges and the aura range of Vex Armor. Ability Duration mods affect the energy drain of Spectral Scream and Effigy and the duration of Elemental Ward and Vex Armor.
So, all things considered, here are some builds you may want to try on your Chroma: