This way they attempt to reproduce the same relative response in the cones as the real colour would. Because the colours of the filters in the monitor don't match the cones' most responsive colours, a small margin of error creeps in. A monitor will therefore never be able to perfectly reproduce something we see with our own eyes. The colour space of an RGB monitor doesn't cover the whole range of the eye. That said, monitors produce a far greater range of colours than the CMYK printing process used in magazines.
Colours appear different when surrounded by dissimilar colours.
This process is called chromatic induction. The way the brain processes information from the eyes produces interesting effects. While the eye passes absolute information to the brain, it's then interpreted in a relative fashion. The hue of a colour is perceived differently depending on which other colours surround it. If you look at the panel on the right, the circles in each row are actually the same colour.