Within a TRADITIONAL STANDARD PLAYING CARD deck (of 54 cards with jokers, as typically printed in a 9 x 6 array), There are only 4 7's within the deck. Out of those, only 2 of them are black ( 7 of Clubs & 7 of Spades).
Non-Traditional standard playing cards decks may choose to utilize different colors for each suit, but will typically utilize dark colors for the "black" cards (like Blue & Green) & light colors for the "red" cards (like Red, Orange & Yellow). These may be referred to as "Four Color" decks for this variation on the standard deck, but would still have 2 "black" 7's.
Please be aware that Pinochle Decks only utilize cards from 9 to Ace & have a double-print of each suit to form a 48 card deck (in a 6 x 8 print array). These decks would hold absolutely NO 7's within it.
Hope this helps!