Phosphor mixes changed over the years. Initially white phosphor was the thing everyone used because TV, you could do grey scale (aka black and white TV) with one phosphor.

This was expensive stuff (relatively as it needed reasonably linear response to beam energy) and in test equipmentment (like oscilloscopes) green phosphor came into use. Both because it was monochrome anyway, and because it had higher "persistence" which was bad for video but good for things where you wanted to see where the beam had been.

I recall when DEC introduced amber phosphor terminals in the mid 70's arguing that they ghosted less (lower persistence) and they were easier on the eyes (less eye strain). Full color terminals followed with the growth of color TVs.