This poem is very simple, but nice. Short and sweet. There are a few small, nit-picky problems though. At then end of the first line, put a comma instead of a colon. "Watch the upside down rainbow as a smile on my face unfold..." This sentence is a little awkward, but you could get away with just changing 'unfold' to 'unfolds'. If you want to make it flow better, I'd change it to something like, "Watch the upside down rainbow as my smile unfolds..." Good job, other than that.
"I don't know half of you half as well as I should like, and I like less than half of you half as well as you deserve."
-Bilbo Baggins, The Fellowship of the Ring, J. R. R. Tolkien
Pardon me, but I'm not too keen on rhetoric and grammar. I do not know much concerning poetry or the sorts. Words, on the other hand, I appreciate. I had once drawn a metaphor to the spirit and a sunflower, I thought it, too, befitting. The eyes longing for something quiet vivid and true as the sunflower seeks her sun. Have you by chance read of Plato's allegory of the sun? I would say such a thinker is much like the eyes you described in your poem. Pardon me again for thinking too much upon the words you wrote. It was a nice poem~~ thank you.