The difference between Unyellow and Yellow

When used as adjectives, unyellow means not yellow (in various senses), whereas yellow means having yellow as its colour.

Yellow is also noun with the meaning: the colour of gold, butter, or a lemon.

Yellow is also verb with the meaning: to become yellow or more yellow.

check bellow for the other definitions of Unyellow and Yellow

Yellow as an adjective:

Having yellow as its colour.
Yellow as an adjective (informal):

Lacking courage.
Yellow as an adjective (publishing, journalism):

Characterized by sensationalism, lurid content, and doubtful accuracy.
Yellow as an adjective (chiefly, derogatory, offensive):

Far East Asian .
Yellow as an adjective (dated, Australia, offensive):

Of mixed Aboriginal and Caucasian ancestry.
Yellow as an adjective (dated, US):

High yellow.
Yellow as an adjective (UK, politics):

Related to the Liberal Democrats.

Examples:

"yellow constituencies"
Yellow as an adjective (politics):

Related to the of Germany.

Examples:

"the black-yellow coalition"

Yellow as a noun:

The colour of gold, butter, or a lemon; the colour obtained by mixing green and red light, or by subtracting blue from white light.
Yellow as a noun (US):

The intermediate light in a set of three traffic lights, the illumination of which indicates that drivers should stop short of the intersection if it is safe to do so.
Yellow as a noun (snooker):

One of the colour balls used in snooker, with a value of 2 points.
Yellow as a noun (pocket billiards):

One of two groups of object balls, or a ball from that group, as used in the principally British version of pool that makes use of unnumbered balls (the (yellow(s) and red(s)); contrast stripes and solids in the originally American version with numbered balls).
Yellow as a noun (sports):

A yellow card.

Yellow as a verb (intransitive):

To become yellow or more yellow.
Yellow as a verb (transitive):

To make (something) yellow or more yellow.