(1) An implementation of the RGB colour model which assumes a linear relationship between the primary colours and the amount of light emitted. The linear-RGB space is both the mathematically most simple and physically most correct implementation of the RGB model, but yields suboptimal results when the human eye and display technology is taken into account. The Grasshopper colour picker does not provide access to the linear RGB space.

(2) A type of distance metric showing the distance between two colours in the linear-RGB unit cube. Identical colours have a distance of zero, while the largest possible distance between colours equals √3, signifying the distance between the opposite corners of the colour cube. Using this metric is ill-advised, since it contradicts the human experience of colour.