The three textboxes on bottom left show the color numbers that often are used in various applications.
Color number decimal and Color number hexadecimal is the number, that is assign to a color by 24 bit color depth. It is calculated with the formula for additive color mix: (Color number) = (red intensity) ∙ 2560 + (green intensity) ∙ 2560 + (blue intensity) ∙ 2562. The both representations of color number are often used in programming languages.
RGB hexadecimal for HTML is built of one after the other written hexadecimal values of red, green and blue intensity. It is used in HTML and many graphic programs.