Open the Game scene and run the game. Select the ScriptsHoleder object in Hierarchy and find the Colors Controller script on it.
Press New button and type preset name. After that press Create and then Load Current buttons.
Adjust all colors as you need and hit the Save to current button.
Exit play mode and drag the newly created preset (it is located in folder Assets/Project Data/Content/ColorPresets/) into the Presets List on ColorsController - now it will be randomly used together with other presets in the game.
To adjust existing presets enter play mode and press buttons with triangles - it will scroll through all items into the Presets List. When required preset is selected - apply changes you need (do not forget to press the Save button when you finished your changes).