A matching number can change the color in play
In Uno, a card can be played when it matches the top discard by color, number, or symbol. So a green seven can cover a blue seven: the shared number makes the play legal, even though the colors differ.
After the green seven lands, the green card becomes the new top card. The next player must match its color or number—so they could play any green card or another seven—or use a Wild card if permitted. The old blue color no longer matters.
The match also redirects the next player
That makes a number match more than a way to get rid of a card. It can shift which color the next player needs, without requiring a Wild card to choose a color. If the next player has no green card, seven, or playable Wild, they may have to draw under the game’s rules.
The useful distinction is between what lets you play a card and what the next player must match: the first can be either the number or the color, but afterward the newly played card sets the target. A single matching number can therefore turn a blue sequence green.
