Real Dictionary

yellow
colour: Something that is yellow is the colour of lemons, butter, or the middle part of an egg.

yellow in American English
of the color of gold, butter, or ripe lemons
noun: a color like that of egg yolk, ripe lemons, etc.; the primary color between green and orange in the visible spectrum, an effect of light with a wavelength between 570 and 590 nm

yellow in British English
adjective: of the colour yellow
noun: any of a group of colours that vary in saturation but have the same hue. They lie in the approximate wavelength range 585–575 nanometres. Yellow is the complementary colour of blue and with cyan and magenta forms a set of primary colours
verb: to make or become yellow