Grind the tomatoes with 1 cup of water and sieve it. Boil 2 cups of water in a vessel. Add the sugar and citric acid in it. When the sugar dissolves, add the tomato juice. Mix the colour in 1dsp of water and add it to the squash. Remove from fire immediately after boiling and allow to cool.
When the solution cools, take 1/4 cup of juice from it and dissolve potassium meta bisulphate in it. Pour this to the remaining squash and stir well. Store the squash in an airtight bottle. The squash can be used after 2 days..