That chart is not showing percents. "#90" is not "90%".
That chart shows the hexadecimal to decimal conversion. The hex number 90 (typically represented as 0x90) is equivalent to the decimal number 144.
Hexadecimal numbers are base-16, so each digit is a value between 0 and F. The maximum value for a two byte hex value (such as the transparency of a color) is 0xFF, or 255 in decimal. Thus 100% is 0xFF.
