What is the name of Rolex's blue luminescent material used on watch dials?

Rolex’s blue luminescent material is called Chromalight.

Chromalight is Rolex’s proprietary blue-emitting lume, applied to selected watch hands and hour markers so the display remains readable in darkness. Unlike older radioactive luminous paints, modern Chromalight is a non-radioactive photoluminescent material: it absorbs light and then releases that energy gradually as a glow.

The blue color is a useful identifying feature, but it is not the same thing as the general term “lume.” Lume describes any luminous material used on a watch, while Chromalight is Rolex’s brand-specific name. Tritium is an older radioactive technology, and Super-LumiNova is a separate trade name used by another manufacturer of photoluminescent pigments.

Rolex introduced Chromalight on the Deepsea diving watch in 2008 and later extended it to other professional and classic models. Its intended advantage is prolonged legibility in low-light conditions, especially underwater, where a diver may need to read the watch after leaving bright surface light.