At some solitaire levels, half of the cards on the table may be shrouded in fog with a few balloons in it.
The balloons have suits in red or black that are sort of a code that you need to "enter" in order to remove the fog and see the hidden cards. Look at the suit and the meaning of the icons, and remove the cards of the same suit from the uncovered part of the table - and voilà! The fog will be removed, and you will be able to continue your level with all the cards.