[Canuck]

Jimmy
I experimented with this a few years ago. I used blue food colouring and Dawn blue dish soap. I used a sponge to brush it across the lettering with good results.
I also called, Kelsey who said their tires came from the plant that way and did not know the source.
I also called Black Diamond who do their own whitewall applications. They said they buy the ‘soap’ in 5 gallon pails from a supplier in upstate NY. I got the name and contacted them but never got a response.
It’s not rocket surgery. Today I cleaned up s set of Eagle ST radials with SOS pads and noticed their blue soap will dry quickly in the sun and leave a blue residue.