Correct, alignment was not a factor for single-phosphor tubes.
The eye is not nearly as sensitive to red and blue so those colors did needed higher energies. But I doubt that it was because the phosphors are cheaper. Computer terminals and monitors were very expensive back then, but commercial color television made some of the common components (like phosphors) relatively cheap.
Green was found to be readable and pleasant. It was the most common for IBM equipment (such as the PC monochrome display).
Amber is very visible, especially in bright light. It was popular too.
The eye is not nearly as sensitive to red and blue so those colors did needed higher energies. But I doubt that it was because the phosphors are cheaper. Computer terminals and monitors were very expensive back then, but commercial color television made some of the common components (like phosphors) relatively cheap.
Green was found to be readable and pleasant. It was the most common for IBM equipment (such as the PC monochrome display).
Amber is very visible, especially in bright light. It was popular too.
White was popular with DEC terminals.