If you are already using the colour red, then use yellow and black. It is a natural warning sign of nature, and will definitely draw attention. It is used also on many danger signs for construction sites.
Is red a danger colour?
In daily life, red is commonly used to convey danger or danger-relevant concepts. Red is the prototypic colour of alarms, sirens, stop signals and warning signs that convey danger and the need for vigilant attention.
What is the color for danger?
Red – indicates (1) danger, (2) stop or (3) presence of fire protection equipment.