orange (adjective, colour term; synonym: yellow-red, brown) – the hue of the visible light spectrum located between yellow and red. The human eye typically perceives monochromatic light with a wavelength somewhere between 570 and 650 nm as orange. Classical colour theory often regards orange as a secondary colour, achieved by mixing yellow and red paint. Modern colour recognizes that no absolute primary colours exist because almost any three or more colours can be mixed to produce all other hues. Therefore, the classical distinction between primary and secondary colour is largely irrelevant. More important is the colour model that is used to generate colours, either by subtraction (using paint or ink that absorb light) or addition (using light sources that emitted light). In both, the additive RGB and the subtractive CMYK model, orange is not used as a primary colour. In the additive RGB colour model, orange is a mixture or yellow (Y) and red (R) light. It can also be achieved as a subtractive mixture using red and green ink. Both red and green are not used as primary subtractive colours in the CYMK colour model. Therefore, using an inkjet printer with CMYK cartridges, orange will be a result of mixing two parts of yellow (Y) with one part cyan (C) and one part magenta (M). Brown is essentially part of the orange colour spectrum, i. e., it is a hue of orange with low chroma. Following these models, orange and brown are not "pure" colour, but both have to be generated by mixing either light or ink. Colour is, however, largely a subjective phenomenon based on human perception. Therefore, there colour orange or brown is certainly no less accurate than their synonym yellow-red and there is no objective reason, to replace either one of these well established names. On the contrary, lichen thalli are often distinctly orange or brown and both term are very useful to refer to these taxa.