Yep that was pretty much the end result.
The yolks could be coloured by adding different colouring, they had pretty much every colour from almost white through to black, (green yolks didn't look very appetising!)
I do remember beetroot being fed as a colouring agent and most of the ingredients were just normal day to day stuff but given in large quantities, there were no secret potions or dodgy stuff fed to them.
Fishmeal was indeed used for one of the taste tests, as well as liquorice, garlic, mint, sugar and a whole load of other stuff I can't remember properly (it was 25 years ago)

But the main purpose of the testing was to check the nutrition levels across the range and there was no difference between breeds, whether commercial or pure breed, I remember both Black and white leghorns, ISA Browns, Ross Broiler breeders and a few others being used.
Neither was there any difference between housing type/system or diets fed, other than colour and taste.
I suppose its a bit like the white vs brown egg thing, we were all told brown eggs were better for us so we believe it, were as in reality there is no difference in nutrition value between them at all.