The difference is not only whether the image has colour — power draw, light pollution and the installation environment all matter.

• Infrared: monochrome, discreet and relatively low power. Suited to perimeters, boundary walls and remote positions where presence, shape and movement are what count.
• Full colour: achieved with a fast lens, a large sensor or white-light LEDs. Colour helps identify clothing and vehicle colour, so it suits entrances, shops and residential lobbies where detail drives the decision.
• The white-light trade-off: continuously lit white LEDs cause visible light pollution and complaints in residential areas. Smart modes that switch the light on only when a person approaches mitigate this.
• Ambient light dependency: full-colour performance tracks the available ambient light. In genuinely dark rural scenes, a full-colour model without white light falls off sharply.

Recommendation: prefer models that support both modes and can switch. Use full colour by day and in ambient light, and fall back to IR in complete darkness — the best balance of quality and cost.