Detectable Warning Surfaces: Color and Contrast

As a provider of cast iron truncated domes through Spruce & Gander, Inc., we are often told by clients that their understanding is truncated domes must be yellow. There is an ADA regulation about contrast to be aware of when selecting color, however yellow is not your only choice in every application. The objective for detectable warning surfaces is that they provide a 70 percent minimum visual contrast with adjacent walking surfaces either light-on-dark, or dark-on-light. Yellow is specified clearly when required.

Here are some examples for California:

  • California Title 24 requires detectable warnings on the full surface of curb ramps with a slope less than 1:15.
  • Detectable warnings on transit platforms, track crossings, bus stops, hazardous vehicular areas and reflecting pools must be safety yellow (Federal Color No. 33538) but for other applications, the 70 percent minimum visual contrast applies.
  • Compliance with the yellow color requirement per Federal Standard 595, Color No.33538 per Caltrans Standard Specifications. Caltrans also requires that manufacturers be on their approved list.

Check with all applicable sources such as local building code (many jurisdictions’ codes based off the International Building Code) to verify requirements.

The concept of contrast leaves room for flexibility. Simple right? Not always, and because many people are unsure about what color to select, they tend to stick with yellow to err on the safe side. I mean, how do we measure contrast anyway?

Here is the formula:

Contrast percent = [(B1-B2)/B1] x 100


B1 = light reflectance value (LRV) of lighter area

B2 = light reflectance value (LRV) of darker area

This formula can best be expressed visually:


In this example, LRV 50 represents concrete, and LRV 11 conservatively represents cast iron which results in excellent contrast, well above the 70% recommended threshold.

So now that we have the formula, how do we determine the Light Reflectance Value (LRV)?

A color's Light Reflectance Value (LRV) measures the amount of visible and usable light that reflects from (or absorbs into) a painted surface. Simply put, LRV measures the percentage of light a paint color reflects.

Light reflectance value LRV is measured on a scale that ranges from zero (absolute black, absorbing all light and heat) to 100 percent (pure white, reflecting all light).


Building and design professionals (everyone from architects and engineers to interior designers and color consultants) use these measurements as guidelines to predict how light or dark a color will appear. The values are also used by lighting designers to calculate the number and type of light fixtures needed to provide a certain amount of light for interior spaces.

The Americans with Disability Act Accessibility Guidelines (ADAAG) recommends a 70% light reflectance value or higher for those with impaired vision, but this is not a strict requirement. There are a number of color combinations in the 60-70% range that work well.

Our experience has shown that 70% is not a magic number. Contrasts of a few percentage points below the recommended figure, depending on the colors chosen, can often yield desirable results.

Another important consideration is how the visual contrast between the detectable warning and the adjacent surface may change over time as materials age. For example, concrete is generally lighter when it is new and darkens over time. Asphalt is generally darkest when it is new and lightens over time. Also, the detectable warning material may fade or darken over time. In the case of cast iron truncated domes, we see they become darker over time staying in good contrast with concrete which also darkens over time.

We proudly represent Urban Accessories. Here are some value adds for choosing cast iron truncated domes over alternatives:

  • Highly customizable; custom radius, cut outs for light ports and bollards, and fewer seams compared to alternatives
  • Avoid dome loss. Cast iron outperforms plastic alternatives, especially in snow areas where shovels, snow blowers and snow plows are used
  • Resistance to salt/chemical/sand applications
  • Avoid delamination and adhesion failure that is typical of surface applied alternatives
  • UV stable, darkens over time vs. losing color and/or peeling away
  • Withstands temperature extremes and variability
  • Differential expansion and contraction compared to substrate

Check out this installation at the Monterey Conference Center in Monterey, CA. Designed by: GLS Landscape Architecture, San Francisco, CA.

For more information, please contact: Spruce & Gander, Inc. (877) 650-7711


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