A colourful, beautiful, and wonderful piece in every way imaginable.
I think this song has one of the best orchestrations I've ever heard on Newgrounds, quite possibly in any song ever. It is so very cohesive and lyrical yet changes so much in under 2 minutes (note how you use the instruments for their colours here and not just their sound). It is so complex and specific yet is light at the same time, never coming across as suffocating in its beauty. If I may say this it is a slice of heaven.
As for the rainbow theme you absolutely nailed it. I have synaesthesia so I can understand how instruments and colours relate better on a more personal level, and I can safely say that you did an *extremely* good job on your choice and use of instruments here even though I may not totally agree with your own assessment. In fact, this is one of a very few songs I've heard where a specific image and theme is captured absolutely perfectly. This is not even the slightest of exaggerations. I could practically feel the rainbow shining through the clouds and rain despite it being sunny where I live.
Lastly I completely agree with you about the symbol rainbow. It is one of the most poignant representations of how life doesn't last, yet your memories always will. This piece is a very beautiful reminder of the joys of life.
Sorry for the long review, but I had a lot to say. What a masterpiece. 5/5, 10/10, favorite forever.
PS:
Troisnyx, do you mind if next year, I review all the songs on tesserakoste on each of their associated days of Lent?