The Rainbow

Afte the flood in the time of Noah, G-d created the rainbow, signifing, that He would not destry the world again.
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The positive concept of a cloud, on a very high spiritual level applies, when spiritual revelations are shining from such a high level, that is impossible for us to receive them [because of our limitations].

Because of this, we need a screening "cloud", through which we will be able to receive the revelation.

This can be learned from the verse, "For a sun and a shield, is Havaye Elokim [the L-rd G-d] (Psalms 84:12)."
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The Divine Name "Havaye", is a transposition of the four letters of the unutterable Divine Name, that refers to unlimited G-dliness, which transcends all the created spiritual levels.

The Divine Name Elokim, refers to the G-dliness, which is contracted, enclothed and concealed, within the spiritual and physical worlds, in order to enliven the creations within them.]

Just as it is impossible to look at the sun without a screening shield, so it is impossible to directly receive the revelation from the transcendent level of the Name Havaye, except by way of the screening shield, of the "covering" of the Divine Name Elokim.
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This spiritual screening, is the positive concept of a cloud, as it is written, "And Moses came within the cloud" [when he ascended to Heaven from Mt. Sinai, to receive the Torah].

Since the revelation of Mt. Sinai was of the highest level, in order to receive this revelation, it was necessary for Moses to be enclothed in the cloud [which G-d provided.
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And this is also the concept, of the cloud of the smoke of the incense, [that was brought in the Holy of Holies of the first and second Temples in Jerusalem] on Yom Kippur; that came through the service of repentance.
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From the cloud of highest holiness, there was brought down (through the 120 different combinations of the Hebrew letters, of the Divine Name E-L-O-K-I-M, in a way of histalshelus) the level of a cloud that hides and conceals completely.

And because of this, clouds are compared to sins.

There are light clouds, through which it is possible to look, and benefit from the sun, even if only for a moment. And there are thick clouds, that darken completely.
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And through this, one can understand the concept of the rainbow, that was newly created, specifically after the Flood.

Before the Flood, the world was not purified.
Therefore the clouds were of a type, which the sunlight could not penetrate; so the sun was not able to be seen through them. Therefore, it was not possible to produce the colors of the rainbow, before the Flood.

This was not the case after the Flood, through which the world was purified. The clouds became purified, and the light of the sun was able to be seen through them, in the colors of the rainbow.
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This type of cloud, which is for the purpose of revelation, also teaches about the concept of repentance. It is similar to the cloud, of the smoke of the incense of Yom Kippur, [when it was brought during the times of the first and second Temples], that come through the repentance of Yom Kippur.
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The above concepts are reinforced by one of the fundamental points of Chassidic philosophy which teaches, that the world is essentially good.

Other approaches teach, that one has to fight against the world to improve it. In contrast, Chassidic philosophy trains us, to appreciate the good in the world, and use it - and all the world - for positive purposes.
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And from this will be understood what is written in the Zohar, "Don't expect the footsteps of Moshiach, until you see a rainbow shining with bright colors."

This is because, the concept of the rainbow, teaches about the service of repentance, as explained above. It is also because, [the rainbow teaches us that the repentance], should be in all the three ways [Kindness, Judgement and Mercy], that are hinted to by the primary colors, as explained above.

Therefore [when you see people turning to G-d in repentance], you can look forward to the footsteps of Moshiach; because Moshiach is the concept of repentance.
Moshiach is destined to bring [even] the righteous to repentance.

Through revealing the spark of Moshiach, that is the microcosm in every, specific person, which is the concept of repentance; then Moshiach will be revealed in the world at large.