I had my small frame parts done in standard white and then spray painted them in a colour nearer to the Ariel colour. I used Rover -- Tudor white, it was near to the colour on my bike when I bought it . Drags have a list of the colours used on their site.
There are some powder coaters who have a range of colours, some are quite near to the Ariel colours, one is south of Birmingham ----Redditch shot blasters ?
Roger will know who they are , he's used them a few times.
Brian H. PS I don't think Ariel were as exact on colours as bike manufactuers are now !