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