How many shades can represent 8 bits per pixel?

If you consider that there are two possibilities for each byte, then taking two to the eighth power gives you 256 different possibilities. If you mean there are a total of 24-bits, then you can take 2 to the 24th power to get the answer, or you can take 256 to the 3rd power. Either way, that should represent about 16.7 million possibilities.