Like all other cattle, bulls are colour blind. The myth that a bull can see the colour red, is just that, a myth. Despite most bull-fighters using a red cape to attract the bull, the fact is that they could use a multi-coloured cape and the bull would still charge at them. The bull is only attracted to the movement of the cape, not the actual colour of it.
In other words, “NOT AGRESSIVE UNLESS PROVOKED”.