Nimitta I
Visible object is a rupa that impinges on the eyesense. It is experienced by seeing-consciousness that arises in a process of citta. Visible object or colour is an extremely small rupa arising in a group of rupas, it does not arise alone. It arises together with the four great elements of solidility, cohesion, heat, motion and other rupas which support it. It falls away immediately and soon after it arises and falls away again. There is not one unit of visible object but countless units arising and falling away. We cannot pinpoint which visible object is experienced at present moment. There is only an impression or mental image ( nimitta ) of visible object. This causes us to think that visible object does not fall away -  just like a touch is swung around very rapidly. In this way, we have the impression of a whole - a circle of light. Visible object impinges on the eyesense and after it has fallen away, what is left is the impression or sign ( nimitta ) of visible object.
Topic 12