You're describing...

The Rainbow Flag

Explanation

Gilbert Baker, encouraged by Harvey Milk, had originally created an 8-stripe rainbow flag, assigning meaning to each color. Your stanzas' themes correspond to each of those meanings:

Stanza 1: Pink = Sex
Stanza 2: Red = Life
Stanza 3: Orange = Healing
Stanza 4: Yellow = Sunlight
Stanza 5: Green = Nature
Stanza 6: Turquoise = Magic/Art
Stanza 7: Indigo = Serenity
Stanza 8: Violet = Spirit

Though a different shape, my form I take
From that which bends but does not break

Though a rectangular shape, it's derived from a rainbow (typically symbolized as an arc).

I have changed throughout the years.
I have seen my share of tears.
But I still shine on, you see

The flag, though changed (from 8 colors to 7, then 6), perseveres. I feel these lines also signify the LGBT community surviving the many struggles it has to go through.

You're describing...

The Rainbow Flag

Explanation

Gilbert Baker, encouraged by Harvey Milk, had originally created an 8-stripe rainbow flag, assigning meaning to each color. Your stanzas' themes correspond to each of those meanings:

Stanza 1: Pink = Sex\Sexuality
Stanza 2: Red = Life
Stanza 3: Orange = Healing
Stanza 4: Yellow = Sunlight
Stanza 5: Green = Nature
Stanza 6: Turquoise = Magic\Art
Stanza 7: Indigo = Serenity\Harmony
Stanza 8: Violet = Spirit

Though a different shape, my form I take
From that which bends but does not break

Though a rectangular shape, it's derived from a rainbow (that's typically depicted as an arc). Also, as per Keyur PATEL's answer, light 'bends' but doesn't break, so this could also allude to its visible spectrum, as it goes through a prism.

I have changed throughout the years.
I have seen my share of tears.
But I still shine on, you see

The flag, though changed (from 8 colors to 7, then 6), perseveres. I feel these lines also signify the LGBT community surviving the many struggles it had to go through.