Humans make up their minds within 90 seconds of their initial interactions with products. Psychologists research shows that between 62-90% of the assessment is based on colours alone.
Red is the most prominent colour in fast food logos. It may be a coincidence, but it may just be that this colour is known to stimulate appetite. Red attracts attention and is associated with increases in energy, heart rate, excitement levels and hunger.
On the other hand, blue is the least appetising colour. When compared with other colours, blue food packaging is pretty low on the list! So, is there any truth in this? You decide.
Singh S, Impact of Colour on Marketing, Journal of Management History, 2006, 44(6): 783-9.