Do you mean Jones of Aberbeeg?
Best known for using NBC blue livery. Very nice.
Indeed, Jones of Aberbeeg were one of the few NBC firms that used blue livery (like East Yorkshire for a short while, Midland General, Sunderland District, etc). They were a former independent (don't know when they were bought or by BET or BTC) and were based in Aberbeeg, with operations centred on nearby Abertillery. The depot is still standing, used as a car showroom, or at least it was last time I was in the area.
They were managed as part of Western Welsh/Red and White, and had vehicles cascaded from those fleets and new vehicles. The fleet eventually had new RE/ECWs and then Leyland Nationals. The last were, I think, the WUH-T batch. All vehicles were numbered in the R&W style system, and this lasted into National Welsh days.
The death knell was the Gwent Vales MAP scheme in 1981, and the depot closed as part of that with operations allocated to Brynmawr, Tredegar and Crosskeys depots of NW and the blue vehicles getting standard poppy red.
I'm sure one of our older Welsh correspondents can provide more information on how they became part of the NBC. Hope this helps