Qualia

When the appropriate region in our visual cortex is activated by strong signals from red cones and green cones in the eye and when no substantial signal from blue cones is present, that is the experience of the color yellow.  Similarly, when Asa H has the appropriate lower level case activated by a signal of value 5.5 coming in from a Lego NXT color sensor, that too is an experiencing of the color yellow. Either of these may also have become associated with simultaneously hearing the word "yellow" spoken. If you receive slightly different strength signals from the cones in your eyes then you experience a slightly different shade of yellow.  If Asa receives a 5.4 or 5.6 from the color sensor then it experiences a slightly different shade of yellow.