The speaker starts with a simple idea: words like happy, sad or angry only scratch the surface of what people feel. As you grow and understand the world better, emotions get stranger and harder to name. You stop being sure how you feel, and you begin to see how the world can hurt you. The speaker says not everyone reaches this point, but those who do recognize cruelty and see what they call the "true colors" of the world.
Then the poem turns. The world, the speaker says, is grey. Anyone who still sees color should be congratulated, a line that sounds half sincere and half bitter. The ending is the most telling part: people who have lived in the grey long for color to come back, and would never take it for granted again. The mood is heavy and disillusioned, but there is a quiet longing underneath, a wish to feel that brightness once more.