Are you talking head color or more generally, eg morning, noon or lights off? I dont go by trich color myself, more on the state of the calyx, if its swollen across the plant, then I pick, I do this early in the morning, as soon as the light pops on.
When and how you choose is personal, perhaps you work and dont have time first thing, other people i know pick on trichs as above and at the end of the day, touting that extra light generates more oil by way of UV protection. This might be true outdoors in the right lamp set up, eg not HPS which lacks UV range.
The reason I pick in the morning? well during the night, or lights off cycle, the plant will sink the sugars it has made during the day, in to the sinks, these being the buds, the blooms the fruits. During the day, the pathways to sink sugars to fruit are disabled, and so it makes no real sense to me to pick at any other time than first thing in the morning. I take me lead from farmers, they get up right early to pick, this is not a matter of allowing time in the day, it is for good reason i suggest regarding quality.
Hope this helps