For Simon, it appears to be this, at least to me:
-Choice 1 - Castlevania box art
-Choice 2 - Red - Simon's Quest
-Choice 3 - Yellow & Black - Christopher Belmont
-Choice 4 - Red & Black - Castlevania Chronicles Simon
-Choice 5 - Blue - Super Castlevania IV Japanese Box Art
-Choice 6 - Purple (with gray hair) - Vampire Killer Sprite colors (this one is kinda reaching)
-Choice 7 - Orange with Red Hair - ?
-Choice 8 - Dark purple (dark brown hair) - ?
As for Richter:
-Choice 1 - Classic Blue - Rondo of Blood
-Choice 2 - Red - Unused "Red" Richter (Castlevania - The Bloodletting)
-Choice 3 - Purple - ?
-Choice 4 - Green - Poisoned Sprite for Richter (Rondo of Blood)
-Choice 5 - Yellow/Brown, Red Bandanna - Julius Belmont (Sorrow series)
-Choice 6 - Blue with Gray lining - Symphony of the Night
-Choice 7 - Gray - "Slowed Down"/"Petrified" Richter (Rondo of Blood and DraculaXX)
-Choice 8 - White/Red - Leon Belmont (Lament of Innocence).
Good guesses, but according to materials I have seen, it's
SimonBrown: Based on Simon's appearance in the Original Mode of Castlevania Chronicles, with some elements taken from his appearance in Super Castlevania IV.
Red: Resembles his appearance in Castlevania II: Simon's Quest.
Yellow: Resembles his appearance on the
Western boxart for Super Castlevania IV. It also resembles Fake Trevor in Castlevania: Symphony of the Night.
Black: Resembles his appearance in the
Arrange Mode of Castlevania Chronicles and his
in-game appearance in Vampire Killer.
Blue: Resembles his appearance on the
Japanese boxart for Super Castlevania IV.
Purple: Resembles Cornell from
Castlevania: Legacy of Darkness. (
Cornell, of all people. Talk about reaching.Orange: Resembles his
in-game sprite in Castlevania (1986).
Indigo: Unknown
RichterDefault: Based on his appearance in Rondo of Blood and Castlevania: Dracula X.
Red: Resembles
Christopher Belmont as he appears in Castlevania: The Adventure ReBirth.
Purple: Resembles the
Dark Priest Shaft as he appears in-game in both Rondo of Blood and Symphony of the Night.
Green: Resembles the
"Curse" status-effect from Castlevania: Rondo of Blood and Castlevania: Dracula X.
Yellow: Resembles artwork for
Johnny Morris for Castlevania: Bloodlines.
Deep Blue: Resembles
his design in Castlevania: Symphony of the Night.
Black: Resembles the
end credits graphics of Castlevania: Dracula X, which were displayed in a monochromatic palette.
(Again, WHAT THE EVER LOVING HELL IS WRONG WITH MARIA IN THAT FRAME?!)White: Resembles
Leon Belmont from Castlevania: Lament of Innocence.