Unfortunately that is old information that hasn't been updated - recent discussion has concluded and agreed that they entered service in corporate blue based on colour photographs, witnesses and as documented in books such as 'Diesel and Electric Locomotives of the Southern Region' by Pallent and Bird who quote "they (JBs) entered service in the blue livery which at the time was beginning to obliterate the last shreds of regional individuality in rolling stock colour". Also check with the SEG. And with the recently repainted 73 in what was claimed to be 'the original electric blue' but on inspection and comparison turns out to be corporate blue.
What needs to be remembered is that at the time of the introduction of JBs and corporate blue there wasn't the paint/pigment technical advances we currently enjoy and many depots had slight variations from the reference colour. For example it has always been considered that the corporate blue used by Eastleigh tended to have a more turquoise hue than others. Plus, of course, the paints of yesteryear were not as stable as current samples and faded or discoloured at lot more quickly and easily. Once the gloss surface was removed by washing machine chemicals and the bleaching effect of sunlight, pictures do appear to show that some 73s were in a strange light blue colour.
Also don't forget that memory has never been a very reliable source of accurate information particularly as many consider that the past was alway much rosier, brighter and sunnier that it really was.