Design a poster radiating a positive and respectful environment. The central visual element should be a large, beautifully flourishing tree with leaves of various colors representing distinct cultures. Each branch should hold symbols, like a book to signify knowledge or an olive branch for peace, from diverse global cultures, detailing the beauty and richness they bring. The background should exhibit a serene, light sky, symbolizing unity, harmony and peace. Place a large text at the bottom, 'Embrace Diversity, Foster Unity', in bold, easy-to-read letters. Be balanced with the use of colors and ensure every element stands out.