In a Puzzle, But Not a Riddle | Riddle #2

Hello there, and I return with another riddle for you to solve!  Sometimes, riddles provide misdirection, and confusion.  However, the trick is to analyze, and to look at every possibility.  In any case, lets see if you can solve this puzzling riddle:

I’m in you,
But not in him,
I go up,
But not down,
I’m in the Colosseum,
But not a tower,
I’m in a puzzle,
But not a riddle.

Do you know the answer?  If you do, or think that you might, put your solution in the comment selection below.  Will I confirmed the correct answer?  Who knows?  Maybe I will, maybe I won’t.  Sometimes, it is better for the answers to remain secretive.

In any case, I hope your weekend is great, and I will be back with more, in the days to come!  Goodbye, and Merry Christmas!

(And yes, I did draw the header photo.  Don’t judge me too harshly.)