Like musical chords, colour can be discordant. Blue is considered by some colour theorists as naturally darker than red, but use a lighter blue with a deep red and a striking discord is achieved. If violet is considered to be naturally darker than green, then using a dark green with a light violet will again create a striking discord. See the effects on the left. Remember, objectively there is really no such thing as a 'bad' colour scheme.
Taste really is a matter of personal preference.
Of real significance is the effect of colour interaction. This is the way in which a hue will appear to change when surrounded by different coloured backgrounds. To understand this place a small area of red on a blue background, then observe the same red on a green. You will notice that the red appears to have been modified. This effect is known as simultaneous contrast - the increase or decrease in intensity and hue of colours when they are perceived in adjacent positions.