118 is lower-case 'v'.
You're not checking "Serial.avaliable ()" before reading your command character, so as has been pointed out, "Serial.read" will return -1.
Your fade value is going to be difficult to enter, because you'll have to find the exact character code you want, and lower levels will be non-printing character codes.
The "else"s are mostly redundant, you may as well just use fall-through - it will save on indentation.
If you keep your code as is (no check for serial available, no fall through) you can just modify your code to wait for the fade value as follows:
Serial.println("Please enter fade value: ");
while (Serial.available() <= 0) ; // wait for next character
incomingByte = Serial.read();
If you’re on Windows you can enter a three digit (0-255 range) fade value using the numeric keypad (press and hold Alt, enter three digits, release alt and press enter).