Iridescence

Iridescence is the rainbow shimmer seen on bubbles, oil films, and beetle wings — color that changes with viewing angle rather than light direction. Genesis approximates it with a 1D ramp sampled by the Fresnel term, so the entire color cycle comes from a single texture.

Video

The camera orbiting an oil-slick sphere so the iridescent rainbow shifts across magenta, cyan, and yellow as the view angle changes while the light stays fixed.

features/iridescence/iridescence-orbit.mp4

View-angle rainbow shift on an oil-slick surface as the camera orbits.

When to use it

Oil slicks and soap bubbles — a full saturated rainbow.
Sci-fi armor — a subtle violet-to-cyan shift under specular.
Beetle shells and jewellery — high-saturation iridescent metals.
Stylized water highlights — colorful caustic flicker.

Difference from Hue Shift

Hue Shift rotates the entire albedo over time. Iridescence shifts color based on view angle, so turning your head changes the color, not time. They can stack for a moving, view-dependent rainbow.

How it works

The shader computes 1 - dot(N, V), raises it to _IridescencePower, and uses the result as the X coordinate into _IridescenceRamp. The sampled color is blended over the surface by _IridescenceIntensity. An optional mask restricts the effect to specific UV regions.

Plain metallic surface with a single tint.

Rainbow shift along the grazing edges, brighter at low view angles.

Off

Iridescence · ramp

A plain metal surface against the same one with iridescence. Drag to compare.

Properties

Inspector label	Shader property	Type	Default	Description
Iridescence Ramp	_IridescenceRamp	Texture2D	None	1D ramp (256x4) sampled by view angle.
Intensity	_IridescenceIntensity	Float (0–1)	0.5	Mix amount against the base lighting.
Power	_IridescencePower	Float (0.1–8)	2.0	Biases the Fresnel curve. Higher confines the rainbow to grazing angles.
Phase Shift	_IridescenceShift	Float (0–1)	0.0	Phase offset into the ramp. Animate for shimmer.
Iridescence Mask	_IridescenceMask	Texture2D	white	UV-space mask limiting the effect to regions.
Blend Mode	_IridescenceBlendMode	Enum	Add	Add, Multiply, Screen, or Overlay.

Usage

Author a ramp in the Ramp Creator. The classic oil-slick ramp runs magenta to cyan to yellow to magenta.
Assign it and set Intensity to 0.3–0.5 for subtle, 1.0+ for full chroma.
Use Power to control where the rainbow appears — 1 covers the whole surface, 5+ only the grazing edges.
Animate Phase Shift from a script for a moving shimmer.


material.SetTexture("_IridescenceRamp", oilSlickRamp);
material.SetFloat("_IridescenceIntensity", 0.4f);
material.SetFloat("_IridescenceShift", Mathf.Repeat(Time.time * 0.2f, 1f));

Tips & gotchas

Use bilinear filtering with clamp wrap on the ramp to avoid hue seams at the edges.
Subtle reads better — 0.2–0.5 intensity is usually plenty; full strength looks like a bug.
Pairs with Specular: the rainbow tints the spec lobe naturally in Add or Overlay blend.
Cost is a single texture sample plus a lerp, so it is negligible on mobile.

Ramp Creator — author iridescence ramps in-editor.
Hue Shift — time-based hue rotation.
Specular Highlights — pair for iridescent metal.
MatCap — an alternate way to fake complex highlights.