This page describes the endings that can be seen in Castlevania II, and how to get them.
Take 15 or more in-game Days to Beat the Game
If you take 15 or more in-game days to beat the game, the ending will be in black-and-white, and...
the text implies that Simon did not survive.
Beat the Game in 8 to 14 in-game Days
If you beat the game in 8 to 14 in-game days, the ending will be in color, and...
the text says that Simon did not survive.
Beat the Game in 7 or Fewer Days
If you beat the game in 7 days or fewer, the ending will be in color, and there is an additional scene after the text.
Also
The endings remind me of Brøderbund Print Shop.