Ok, I bought a bunch of Conti tubes from Merlin 6 months ago. Black Butyl Rubber.

Cross 28, (25/35) boxed, "Made in China" printed on box and tubes. White lettering. Black cap. Stepped nut.

Race 28, (18/25) bagged, "Made in China" printed on tubes. White lettering. Black Cap. Stepped nut.

I thought I had a couple of Conti tubes of unknown age/providence with yellow lettering, and a bit more texture to the tubes. I'll see if I can find one.