The Hazardous Materials Identification System (HMIS) Color Bar is similar (but not identical) to the Fire Diamond. The HMIS is a hazard rating system that uses color bar labels to identify and provide information about chemical hazards. It was developed by the National Paint Coatings Association (NPCA), now known as the American Coatings Association (ACA).

The Fire Diamond was created by the National Fire Protection Association (NFPA).

The fire diamond is designed for emergencies when information about the effects of short, or acute, exposure is needed.

The color bar is not for emergencies.  It is used to convey broader health warning information.

The HMIS Color Bar is an attempt to convey full health warning information to all employees while the NFPA Fire Diamond is meant primarily for fire fighters and other emergency responders.

Many workplaces use the same rating systems for both.

Both the Fire Diamond and Color Bar systems were developed at a time when there was no mandated labeling system for communicating hazards of workplace chemicals.  The U.S. Occupational Safety and Health Administration (OSHA) only required that a system be used, but did not specify a format.

What the HMIS Color Bar represents has evolved over time.  The  modern HMIS Color Bar is color-coded with blue indicating the level of health hazard, red for flammability, orange for a physical hazard, and white for Personal Protection. The number ratings range from 0-4.

Blue (Health)

The blue section conveys the health hazards of the material. In the latest version of HMIS, the Health bar has two spaces, one for an asterisk and one for a numeric hazard rating. If present, the asterisk signifies a chronic health hazard, meaning that long-term exposure to the material could cause a health problem such as emphysema or kidney damage.

4. Life-threatening, major or permanent damage may result from single or repeated overexposures (e.g., hydrogen cyanide).
3. Major injury likely unless prompt action is taken and medical treatment is given.
2. Temporary or minor injury may occur (e.g., diethyl ether).
1. Irritation or minor reversible injury possible.
0. No significant risk to health.

Red (Flammability)

For HMIS I and II, the criteria used to assign numeric values (0 = low hazard to 4 = high hazard) are identical to those used by NFPA. For HMIS III, the flammability criteria are defined according to OSHA standards, which add elevated flammability ratings for aerosols. HMIS II descriptions, excluding the new aerosol criteria, are shown below.

4. Flammable gases, or very volatile flammable liquids with flash points below 73 °F (23 °C), and boiling points below 100 °F (38 °C). Materials may ignite spontaneously with air (e.g., Propane).
3. Materials capable of ignition under almost all normal temperature conditions. Includes flammable liquids with flash points below 73 °F (23 °C) and boiling points above 100 °F (38 °C), as well as liquids with flash points between 73 °F and 100 °F.
2. Materials which must be moderately heated or exposed to high ambient temperatures before ignition will occur. Includes liquids having a flash point at or above 100 °F (38 °C) but below 200 °F (93 °C) (e.g., Diesel fuel).
1. Materials that must be preheated before ignition will occur. Includes liquids, solids and semi solids having a flash point above 200 °F (93 °C) (e.g., Canola oil).
0. Materials that will not burn (e.g., Water).

Yellow/Orange (Reactivity/Physical Hazard)

Reactivity hazards are assessed using the OSHA criterion of physical hazard. Seven such hazard classes are recognized: Water Reactives, Organic Peroxides, Explosives, Compressed gases, Pyrophoric materials, Oxidizers, and Unstable Reactives.

4. Materials that are readily capable of explosive water reaction, detonation or explosive decomposition, polymerization, or self-reaction at normal temperature and pressure (e.g., chlorine dioxide, nitroglycerin).
3. Materials that may form explosive mixtures with water and are capable of detonation or explosive reaction in the presence of a strong initiating source. Materials may polymerize, decompose, self-react, or undergo other chemical change at normal temperature and pressure with moderate risk of explosion (e.g., ammonium nitrate).
2. Materials that are unstable and may undergo violent chemical changes at normal temperature and pressure with low risk for explosion. Materials may react violently with water or form peroxides upon exposure to air (e.g., potassium, sodium).
1. Materials that are normally stable but can become unstable (self-react) at high temperatures and pressures. Materials may react non-violently with water or undergo hazardous polymerization in the absence of inhibitors (e.g., propene).
0. Materials that are normally stable, even under fire conditions, and will not react with water, polymerize, decompose, condense, or self-react. Non-explosives (e.g., helium).

White (Personal Protection)

This is the largest area of difference between the NFPA and HMIS systems. In the NFPA system, the white area is used to convey special hazards whereas HMIS uses the white section to indicate what personal protective equipment (PPE) should be used when working with the material.

A more complete guide is located here, http://www.ilpi.com/msds/ref/hmis.html

What is the HMIS Color Bar?