Explain how a color motif is used in Macbeth and why is it important.I'm planning to compare Macbeth and another novel through the use of colors....

In Act I of Macbeth as Lady Macbeth
reads her husband's letter, she remarks,

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Yet do I fear thy
nature;

It is too full o'the' milk of human
kindness

To catach the nearest way....
(1.1.17-18)

This is another
use of the imagery of white as symbolic of weakness to
accompany one that has been previously mentioned.  Later, in this same scene, Lady
Macbeth, calling upon the spirits, asks that her milk be taken for gall; that is, any
kindness in exchange for bitterness.

In the final scene of
Act I, after Macbeth expresses reluctance to harm Duncan who has honored him lately,
Lady Macbeth chastises him for being a coward using the color
green:

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Was the hope
drunk

Wherein you dressed yourself?  Hath it slept
since?

And wakes it now, to look so green and
pale

At what it did so freely?  Art thou
afeard

To be the same in thine own act and
valor

As thou art in desire? 
(1.7.38-41)

And, again, Lady
Macbeth employs milk imagery (white) as equivalent to
weakness as she speaks of taking the baby "that milks me" and "dashed the brains
out."

The colors of silver and
gold are used in alluding to the king, Duncan as Macbeth
repents his act of murder.  These colors represent both strength of character and
royalty:

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...Here lay
Duncan,

His silver skin laced with his golden
blood

And his gashed stabs looked like a breach in
nature

For ruin's wasteful entrance:  there, the
murderers,

Steeped in the colors of their trade,
....(2.3.123-127)

Of course,
the play is replete with red imagery as the blood motif runs throughout
Macbeth.  Black, too, connotes death and evil.  One example is in
Act III before Banquo's death, as Macbeth says, "Whiles night's black agents to their
preys do rouse...(3.2.58) And, in Act IV, there is music and a song entitled "Black
Spirits."