It was a BR brand originally (and I believe the copywrite/trademarks are still owned by the government/DfT - the Arriva Trains Wales franchise agreement included a license to use the Alphaline brand but they clearly opted not to make use of it) but as far as I am aware only W&W/W&B/Wessex ever used the brand as part of the external livery. I think in BR days the brand was restricted to a logo in the timetable and TV adverts but my knowledge of BR days is very limited.
Silver & Yellow, would that be
this one? If so, I understand from other forum discussions that the first two 158s painted in silver with the large 'A' logo had those yellow areas on the sides, after which the yellow was dropped (both units, 158745 and 746, went to Wessex Trains and had the blue doors changed to Wessex maroon). Other than 745 and 746, I cannot however find any pictures of a 158 in Alphaline blue & silver except with 'Alphaline Wales & Borders trains' on the side. I would be very greatful if somebody could provide a link to a picture with 'Alphaline Wales & West' on the side (other than the two units with yellow) as it would prove my memory isn't playing tricks on me.