>>>I did find one adjustment so far. The last line should be:
>>>
>>>

>>>	pair2Y = rgb(pair2Yred, pair2Ygreen , pair2Yblue )
>>>

>>>
>>>This fixes that line but still results in another color than the one expected.
>>
>>While reading this thread I was about to propose something similar, but not using the difference (specially that your pair2 plus the difference may go over 255). I'd go with
>>
>>newR2=newR1*(oldR2/oldR1)
>>
>>and same for G and B.
>>
>>You could maybe achieve a similar result by taking the average of the quotients for each R, G and B.
>
>
>Ok, but newR2 may go over 255 as well

I keep thinking about that... some adjustments would be required, to keep it proportional within the 0...255 space. I can't think of the proper math at the moment, all I see are dots in intervals and some geometrical representations.

Perhaps taking the average (geometrical?) of the three quotients? Or solving for the RGB matrix (as in GDI+) which turns the Pair1x into Pair1Y, then apply the same matrix to Pair2X? It's a rather simple 3x3 system of linear equations... um, not... it has 6 variables :).