There is not much more iconic on a construction site than a yellow hard hat and bright orange safety vest. Have you ever driven by a construction job site and wondered why is everything so brightly colored? Why is everyone wearing these bright vests and shirts? Why is all the equipment yellow?
Construction workers wear fluorescent yellow, green, or orange PPE such as vests, shirts and other clothing for safety and visibility. Similarly construction equipment and signs are typically painted a high-visibility color such as yellow or orange for the same attention grabbing safety reasons.
High-Visibility Color Study
In a field study, to determine at what distance certain colors could be seen, participants were asked to look through a shutter while approaching a mock work zone and indicate at what distance they could first identify the various safety colors. 
- The study tested 11 Colors:
- Fluorescent Green
- Fluorescent Yellow
- Fluorescent Yellow-Green
- Fluorescent Yellow-Orange
- Fluorescent Red-Orange
- A combination of Fluorescent Red-Orange with Yellow-Green
- Fluorescent Red mesh over white background
- Fluorescent Pink
- Non-Fluorescent Yellow
- Non-Fluorescent Orange
- Semi-Fluorescent Yellow
Detection distances were recorded for each color and the Fluorescent Red-Orange was the winner of the highest average detection distance. Close behind was Fluorescent Yellow-Green, the combination Red-Orange with Yellow-Green, and the Fluorescent Red mesh. The study recommended any of these colors to be worn in safety clothing with the exception of the red mesh as there are concerns it would not perform as well if worn over a darker shirt.
Check out this quick 3 minute video of why Chartreuse (Fluorescent Yellow-Green) is the most visible color:
It is common practice in Commercial Construction and typically a safety or contractual requirement from General Contractors and Project Owners that high-visible colors and reflectors are incorporated into tops such as safety vests, shirts or jackets. Depending on the construction type and hazards present they can also be incorporated into clothing articles such as pants, rain suits, coveralls, hard hats, etc. With the inherent dangers of passing cars and night work, you are more likely to see road workers in full yellow reflective suits than a commercial plumber on a new building who will typically only be required to wear a vest or t-shirt.
OSHA requires workers especially around traffic to wear additional high visibility in the way of reflective stripes. ANSI has 3 classes (1, 2, & 3), with a class 3 being the most visible and requiring the largest garment background material and reflective material amounts, both measured in square inches. See the ANSI 107-2015 standard for more information.
Is Construction Equipment required to be Yellow?
Yellow, being both highly visible and synonymous with “Caution” and “Warning,” has become the Go-To color for many construction equipment manufacturers (think Caterpillar & Hyundai yellow and black), over the years but it is not a requirement or even a written standard. Even John Deere has dropped their trademark John Deere Green in their construction equipment line and opted for the more traditional Yellow. However there are still many manufacturers such as JLG, Hitachi, & Kubota (Safety Orange), and Sunbelt Rentals who paints all their equipment a bright green. I once worked for a contractor who exclusively rented equipment from Sunbelt Rentals and I liked it as the green was actually a contrast to the sea of yellow and you could easily identify your forklift that the rouge electrician decided to drive across site.
 Dan Turner, J. D., Simmons, C. J., & Graham, J. R. (1997). High-Visibility Clothing for Daytime Use in Work Zones. Transportation Research Record, 1585(1), 1–8. https://doi.org/10.3141/1585-01