Your API key ( https://steamcommunity.com/dev/apikey ) to put in var YourAPIKey
Your Steam ID ( https://steamdb.info/calculator/ ) to put in var YourSteamID

Meaning of color:

Red color mean that you already own the game. (100% accurate, if it's in red you already own it.)
http://image.noelshack.com/fichiers/2018/45/4/1541665959-3.png

Orange color mean that you may already had a version of this game. (Pretty much accurate, if it's in orange you probably own it.)
http://image.noelshack.com/fichiers/2018/45/4/1541665959-2.png

Fuchsia color mean that you own games with similar names. (not accurate at all, if it's Fuchsia you probably own a game from the same franchise or looking on a game with common name but if you hover the title with your cursor you will be able too see the full list of game that trigger this... but be care full The devil is in the detail)
(game owned but not in red because "game of the year" is not in the title on humblebundle)
http://image.noelshack.com/fichiers/2018/45/4/1541667965-this.png
(actual false positive)
http://image.noelshack.com/fichiers/2018/45/4/1541668862-sans-titre.png

Green mean not in the steam library.