As said in the previous answer, a computer monitor that claim to produce millions of colors can actually produce those colors but not at the same time.
Theoretically, a monitor can produce RGB combinations in Red, Green, and Blue which results in a number 16.7 million. ie: 256 colors of red, green and blue make the number like this: 256 x 256 x 256 = 16.7 million. But a normal monitor can only produce a maximum of one or two million pixels. So only about thousands of colors are produced on a monitor at a time.
So as a one-word answer we can tell a PC screen can produce 16.7 million colors!