Slice cucumber lengthwise and scoop out seeds. Chop cucumber and add to food processor with chopped onion.
Puree in food processor. Scoop out pureed cucumber and onion and wring out any excess moisture with paper towels. Return cucumber and onion to food processor. If not using a food processor, you can grate cucumber and onion - be sure to press out any excess moisture.
Add in cream cheese, mayo, salt, and cayenne pepper to food processor. Puree until smooth. Stir in a drop or two of green food coloring if desired.
Keep spread chilled until ready to serve. Garnish with fresh herbs.