Inspired by B by StrawberryClock.
The background of the page can be any color from the rgb spectrum. Colors from the rgb spectrum take on three values (r = red; g = green; b = blue), all with a range from 0 to 255. So the number of possible background colors is:
That is more than the average human eye can differentiate.
The B, too, can take any color from the rgb spectrum. The color it takes is independent from the background color, so the number of possibilities grows exponentially:
That is about twice the number of cells in the average human body.
The B can also take on various shapes and sizes. The font family is the default typeface that the user agent assigns to one of the generic font family names defined by css: sans-serif, cursive, fantasy, and monospace. The font size of the B can be 10 to 50 em (in which em is the default font size of the user agent).
If you multiply that with the number of possible color combinations, you get:
We can now safely assume I have never seen any of the combinations you might have seen.
One might argue that if both the B as its background take on the same color, the font size and family are no longer relevant because the B would be invisible to the human eye. In said case one should subtract one font size - family combination for every color, like so:
Apart from the fact that this hardly makes a difference, we established earlier that the number of possible colors already exceeds that which the average human eye can differentiate. This differs from person to person. Now if we also take into account other variables like the limitations of the display screen, et al. it becomes increasingly difficult to tell which combination should be counted and which should not.
—ACJ's deIdee