I see the current use of a rainbow as a sign of rebellion against God by the LG HDTV community (and those fallen former heavenly host who influence them).
As you mentioned, God's promise not to destroy the earth again by flood after the inter-breeding in (Genesis 6: 1-5, Jude V6, and 2 Peter 2: 4-5) is symbolized by the rainbow... So I certainly see the adoption of the rainbow by those who live in sexual sin as a way to thumb their nose at our Creator. It is a taunt that I don't think is going to play out too well in the end for them.
Then there is the whole "pride" thing... the original sin.