I came across the following line
hsb.s = max != 0 ? 255 * delta / max : 0;
It is called the Conditional Operator (which is a ternary operator).
It has the form of: condition ? value-if-true : value-if-false
Think of the ? as "then" and : as "else".
Your code is equivalent to
if (max != 0)
hsb.s = 255 * delta / max;
hsb.s = 0;