Copyright (c) 1970 Alexander Randolph - Stancraft Products

Dozo is a game played on a 7-side equilateral triangle board (with 28 cells) and with 4 sets of 7 stones of the same colors (a total of 28 stones). 

DROP - Each player must drop a stone of any color into an empty cell.
GOAL - To place a stone which forms an equilateral triangle with two other stones of the same color.
An example

The next player can win by dropping a green stone at cell [1] or a blue stone into cell [2].

Another example

The next player wins by dropping a red stone at [1], making a equilateral red triangle.

There is, at least, another way of winning? (select the next text to find the answer: drop a yellow stone at the bottom right corner

It seems unlikely the game ending without a player making a winning triangle but I do not know an argument (if any exists) that proves it.