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Rainbow Color Cycle (Seamless HSL Color Loop Expression)

About This Expression

This expression creates a smooth, continuous rainbow color cycle by animating the hue value in HSL (Hue, Saturation, Lightness) color space. Instead of jumping between colors or manually keyframing gradients, it mathematically rotates through the entire color spectrum.

Because only the hue is animated—while saturation and lightness remain constant—the color shift feels clean, balanced, and visually pleasing. There are no harsh transitions, no visible loops, and no color banding.

It’s one of the simplest ways to get a perfect chromatic animation with zero keyframes.

How the Color Logic Works

  • Hue Rotation
    The hue value continuously increases over time and wraps back to 0 after reaching 1.
  • Constant Saturation & Lightness
    Saturation is kept at full intensity, and lightness stays neutral, ensuring vivid colors without washing out.
  • Seamless Looping
    The modulo (% 1) ensures the hue loops smoothly without snapping.
  • RGB Conversion
    The final HSL value is converted back into RGB so After Effects can display it correctly.

Expression

// Apply to Color property
speed = 1; // Cycles per second
hsl = [time * speed % 1, 1, 0.5, 1];
hslToRgb(hsl);

How We Use This Expression

Step 1: Select a Layer With Color

This expression works on:

  • Shape layer Fill Color
  • Shape layer Stroke Color
  • Text Fill Color
  • Effect Color Control

Select the layer and property you want to animate.

Step 2: Apply the Expression to Color

  1. Reveal the color property
  2. Hold Alt (Windows) / Option (Mac) and click the color stopwatch
  3. Paste the expression
  4. Click outside the editor to apply

The color will immediately begin cycling through the rainbow.

Step 3: Control the Speed

Adjust this value:

speed = 1;
  • 0.2–0.5 → slow, ambient color drift
  • 1 → smooth, noticeable rainbow loop
  • 2+ → energetic, flashy cycling

The animation always loops perfectly.

Step 4: Use With Multiple Layers

When applied to multiple layers:

  • All layers follow the same color logic
  • Offset their start time or layer in-point for variation
  • Or combine with index-based offsets for staggered rainbows

No extra expressions needed.

Step 5: Enhance the Visuals

For best results, pair this with:

  • Glow for neon or light effects
  • Blur for soft gradients
  • Opacity or Scale pulses
  • Masks or track mattes for animated reveals

The expression handles color; effects add style.

Best Use Cases in After Effects

  • Logo reveals & branding motion
  • Neon titles and outlines
  • UI accents & indicators
  • Music visualizers
  • Social media loops
  • Futuristic or playful designs

Why This Expression Is So Useful

Animating hue instead of RGB values avoids messy transitions and guarantees:

  • Perfect loops
  • Consistent brightness
  • No keyframes
  • Infinite duration

It’s mathematically clean and visually smooth—ideal for both subtle design accents and bold animated graphics.

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