Spectrum

Spectrum is an uncredited 1975 game published by Intellect Games.

I was unable to find the entire ruleset and tried to reconstruct the game rules from the available information (if anyone have them, please let me know).

The game is played on a 10x10 board, with sets of six red and violet pieces, 16 orange and blue pieces, and (probably) 28 green and yellow pieces, for a total of 100 pieces. One player owns the red, orange and yellow pieces, while the other owns the green, blue and violet pieces.

The game starts with both players placing, in alternate fashion, their six red and six violet pieces in the board. These pieces must not be adjacent to each other.

Then each player, on her turn, drops one friendly piece on an empty square provided that it is only adjacent to pieces of adjacent colors in the color spectrum:

red ↔ orange ↔ yellow ↔ green ↔ blue ↔ violet

I'm assuming that a player passes if she has no legal moves; and the match ends after two consecutive passes.
 
Wins the player with more placed stones; or if both players have an equal number, the match is a draw.

Ralf Gering said about this game: The game appears to be flawed because the final scores are always very close (+/- 1). In fact it seems that the best the second player can achieve is a draw. Maybe the game can be fixed by multiplying the number of tiles of the remaining colors. The player with the smaller product wins.