The emphasis of this icon is on the Good News. St Gabriel says it explicitly to Zachariah: he has been sent to announce "good news" (Luke 1:18-19). The text is in the parchment in his hand. John the Baptist himself is good news, announcing the coming of Christ. He called himself "the voice crying in the desert" (John 1:23) because in the Bible, the desert expresses a situation of silence. See for example Hosea, "I will lead her into the desert and speak to her heart". (Hos 2:16). It is an attentive, listening silence. He too brings good news to those who know how to listen.
The mantle of the two Saints is green, symbolising Life, like spring, and symbolising Hope. The blue symbolises Wisdom and Faith. Wisdom = the gift of tasting God and Faith, the gift of advancing in this wisdom. As the angel is a heavenly creature, his garment is richer: red = the love of the Holy Spirit, and gold = light.
Both hold the messenger's staff surmounted by a cross, because the Good News passes through the cross of Jesus Christ to lead to an imperishable NEW LIFE. The wings are there simply to express the speed of the message.
Sister Marie-Paul