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From what I understand, redshift is not something you can easily observe "visually"..
Most astronomical sources like stars emit LARGE bands of electromagnetic radiation, far wider then just the narrow "visible band" of the whole spectrum.
When something is red shifted, the WHOLE emission is shifted to the RED side of the spectrum.
As an example, that means visible RED emissions can red shift into the INVISIBLE infra red (this is actually AWAY from red, but it is towards the red END of the spectrum, as opposed to the blue end).
On the other end, the violet moves into the blue AND the previously invisible ULTRAVIOLET part of the emission moves INTO the visible part of violet.
All that has happened is that the WHOLE spectrum has shifted to the right, so the NET effect on the "WIDTH" of visible light is actual ZERO.
Now if that was the case, then HOW the hell could you know that red shift has even occurred?
Well, it is because the EMISSION BANDS of most atoms are very well known and it is those bands that give away the clue. If you can imagine that the --- below is a full visible spectrum of hydrogen and the full stops are little gaps in the spectrum that are visible with a spectrometer. A normal hydrogen's emission on earth looks like this (for example only):
BLUE----.-----.-.-.---------..-----RED
Then a RED shifted emission line will look like this:
BLUE-------.-----.-.-.---------..--RED
But visibly, they may not look very different at all...
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