What colors or elements of nature does the Friar discuss in his monologue?

Friar Lawrence delivers a monologue (a speech that he says aloud to just himself -- so, really, a speech given directly to the audience) in Act II, Scene 3, before Romeo walks in. The Friar talks a little more, finishing up his monologue, and then greets Romeo. This whole monologue is about nature, especially the power of natural herbs to heal and hurt the body.

He starts by talking about the clouds, the sun and its morning light, and the dew, as well as the disappearing night:

"The gray-eyed morn smiles on the frowning night,

Checkering the eastern clouds with streaks of light,

And fleckled darkness like a drunkard reels

From forth day’s path and Titan’s fiery wheels.

Now, ere the sun advance his burning eye,

The day to cheer and night’s dank dew to dry,"

Then he talks about filling up the basket he's carrying with both poisonous weeds and healing flowers:

"I must upfill this osier cage of ours

With baleful weeds and precious-juicèd flowers."

Next, he compares the earth to a grave and a mother's womb. He talks more about the herbs that come out of the earth, which, like children, are both useful and diverse:

"The earth, that’s nature’s mother, is her tomb.

What is her burying, grave that is her womb.

And from her womb children of divers kind

We sucking on her natural bosom find,

Many for many virtues excellent,

None but for some and yet all different."

He mentions the power and grace of "herbs, plants, [and] stones," and then says that any herb growing in the earth that seems poisonous also has some good quality, but that helpful herbs can also be used for harm:

"For naught so vile that on the earth doth live

But to the earth some special good doth give.

Nor aught so good but, strained from that fair use

Revolts from true birth, stumbling on abuse."

After Romeo comes in, as if finishing his thoughts, the Friar gives an example of a plant with both good and bad qualities. He talks about a particular flower he's holding, saying it can either be poison or medicine depending on whether you smell it or taste it:

"Within the infant rind of this small flower

Poison hath residence and medicine power.

For this, being smelt, with that part cheers each part;

Being tasted, stays all senses with the heart."

Although the Friar mentions many descriptions of shade and light (such as darkness and murkiness), the only color he directly mentions is gray:

"The gray-eyed morn smiles on the frowning night"

That's how the Friar starts his monologue. What he's really saying is that the sun is rising because it's early morning, but he's expressing that thought by imagining that the morning, which has gray eyes, is smiling at the night, which frowns.

Mentioning that the morning has gray eyes focused on the outgoing nighttime, and observing "streaks of light" and "fleckled darkness" helps the Friar express the dual, competing elements of nature, which is appropriate considering how he keeps coming back to the idea that all herbs (and people) have both good and bad inside them.

All of this figurative speech about nature -- especially the reverence with which he shows the natural world -- helps to characterize the Friar as an unusually insightful character, deeply connected to the earth, and knowledgeable about ways to heal and poison people.