What is colour temperature?
The visible colours of light and LED lighting are usually expressed as colour temperatures which are measured in kelvins (K).
Variations of white light are more commonly expressed as warm white, daylight or cool white light which relate to a range of colour temperatures. LED technology is available in the widest range of colour temperatures and wavelengths.
Warm white light could have a colour temperature of between 2700K-3000K (left), daylight falls between 5000K-6000K (middle) &  cool white 6000K-7000K(right). There is no international standard to define these colours, hence the ranges just mentioned & colour temperature will vary slightly by definition depending on the manufacturer of the LED.
 

Which colour LED best suits my application?
Choosing the correct colour temperature is critical factor for the look, feel & application of any area. Warm white sets a more relaxing mood & is best suited for bedroom/lounge areas, whilst daylight & cool white light are better for office/workspace areas where clarity is more essential. Cool white can compliment modern finishes & also works well in kitchens/bathrooms/laundries. It is also important to keep colour consistency so try to stick to one colour in open plan living/dining/kitchen areas otherwise the lighting can clash.
Note that there is a consistent understanding that a cool white LED will produce between 5%-10% more lumens than a warm white LED of equivalent power & this is reflected in the image below. The cool white can also appear blueish when juxtaposed with warm white or daylight but when viewed by itself it appears more white.