Crimson
Offense: ability strength/duration or weapon critical support. Strong on ability-scaling frames such as Mesa, Wisp, and Protea.
Amber
Utility: casting speed, parkour, energy-orb effectiveness, or starting energy. Excellent quality of life on nearly any caster.
Azure
Defense/resources: health, shields, armor, energy, or regeneration. Helpful on energy-hungry frames and armor-based tanks.
Violet
Crimson + Azure fusion. Supports electricity, melee critical damage, and equilibrium-style health/energy loops; good for melee casters.
Topaz
Crimson + Amber fusion. Rewards heat, blast, and radiation interactions; useful on frames that apply those effects reliably.
Emerald
Amber + Azure fusion. Notable for corrosive-stack support and toxin/status play; popular on Saryn and armor-stripping weapon platforms.
Tauforged
Tauforged shards provide stronger versions of the same effects. Use Coalescent Fusion when available, and reserve scarce shards for builds you play often.