you will see fresh food waste turning dark brown first and then black. No trace of green, red, white, orange or yellow is visible anymore.
Not just the look, the texture or the smell of the material, the very nature of it changes beyond recognition. The C:N ratio decreases, pH neutralises, the amount of humus increases and the exchange capacity of the material increases. Uniformity in colour and crumbly texture begins to emerge as the biological activity begins to ebb away and the energy that was so visible during the active phase of composting begins to mellow. All the energy is now stored in the compost and the microbes that are still alive and busy breaking down stubborn substances like woody materials which are high in lignins.
An excerpt from ‘Endlessly Green: Solid Waste Management for Everyone’. Page 200-201.