Your quite right they all got it wrong. Executive and swallow are totally a different livery. Executive grey is a very dark brownish grey almost black swallow Is a very dark purple tinted grey. However this grey was also used on late exec stock. For there are both early and late executive liveries some versions in betwean especially on 86 87 47.
The early executive livery as produced by farish at first correctly and later they did various versions regarding font style and roof band style both correct and incorrect versions were most right but very rare in real life I've only found photo evidence for 4 complete sets and apparently they worked the gatwick service hence the name executive livery as the service was aimed at business men and was one of the first deveations from corporate blue livery. This early executive livery was correctly produced by lima too for a different set the yellow extends over the side grills and the locos had 253 numbers on the nose and the original hollow intercity font style from the blue era. The second set had hollow font and no numbers on the nose the third set had solid font for intercity and a hypen and I think the 4th set had intercity in solid white with no hyphen.
These 4 sets first ran in this early executive livery from 1983 on to about 85 and then the late executive style as also produced only by Lima till now.
There were other differences the shades of red executive wore rail red as on red stripe locos but the swallow livery used intercity claret a deeper red less orangey roofs were black on both liveries never grey as modeled by Dapol Hornby and Bachmann only farish lima nailed this until dapols recent stuf seems to get the livery right. The late exec locos and early swallow locos mixed these shades and you could find early swallow locos with executive shades these also tended to have yellow horn grills and light trims as on 43150 and 43151,
I hope Dapol produce the early exec livery it also differed by having all the roof grills of the hst and the roof sides of the mk3 coaches painted intercity fawn this also has caring shades betwean liveries. Then there are the two other intercity liveries intercity mainline for mixed traffic like on 90s 37s 47s and intercity unbranded as on 47s so all in all there is a lot more to it than it seems. And whoever does research for Hornby needs to do a better job as they call swallow or swift livery executive livery which it isn't, swallow livery represents to me the death nail of british rail it was sectorisation and privatisation preparation it did not carry the arrows of indecision. The last true british rail livery was executive livery and intercity blue, for me happier times indeed and in my view the best liveries ever applied to modern trains. Hope this info helps some out there