I have an Excel spreadsheet that might be of use to you.

Basically, you pick a few pixels from source (A) and enter the "observed" YUV values into the spreadsheet. You then take the YUV values for the same areas from source (B) and enter the "target" YUV values - what the colours should be. You then adjust various parameters (using Excel's Solver if you wish) to get the observed and target as close as possible.

These parameters can then be exported to a ColorYUV command in AviSynth.

The procedure works best with test cards which have large areas of solid colour. A complex picture may be harder to match.