Place cream cheese in a bowl and mash with a fork until smooth. Wrap cucumber in cheesecloth, then squeeze out and discard juice. Add cucumber to cream cheese and mix thoroughly. Wrap onions in cheesecloth and squeeze juice into cream cheese mixture, then discard onions. Mix mayonnaise and Tabasco sauce into cream cheese mixture. Season to taste with salt, then add 1 drop food coloring and mix well. Serve on thinly sliced white sandwich bread, topped with another slice of bread, trimmed, and cut into finger sandwiches.