Complex sentence: Uniforms for public high schools and private schools vary widely in pattern and colour mostly the official colours of the school, but usually consist of material suited to the tropical climate (e.g. cotton).
Split into simpler sentences: Uniforms for public high schools and private schools vary widely in pattern and colour, but most often are in the official school, colours. The material for these usually loose uniforms is often light and suited to the country's tropical climate (e.g. cotton).