Two different ways of making colour
Screens create colour with red, green and blue light. Printing presses create colour with cyan, magenta, yellow and black ink or toner.
RGB can display colours that CMYK cannot physically reproduce.
Which colours change most?
Bright blues, fluorescent greens, vivid oranges and strong purples are often the first to shift during conversion.
What should designers supply?
For predictable commercial print, artwork should normally be supplied in CMYK.
We can convert RGB files, but it is better for the designer to see the conversion before the final PDF is supplied.
The screen is a guide
Monitors and phones vary enormously. The printed sheet is the final result and should be judged under sensible lighting.