NFPA 704
100

The color BLUE represents this.  

What is Health Hazard?

200

The color RED represents this.  

What is Fire Hazard? 

300

Not 6...7... the range of numbers only goes this high.   

What is 4?  

400

Special Hazards are noted in the color.  

What is white? 
500

Don't use this, is represented with a W with a slash through it. 

What is water.