There are not any particular quality-measuring or standardized color-grading for sapphires, this makes a selection of high quality sapphires a rather subjective process. Yet, sapphires which possess certain features are considered to have higher quality and more value. For e.g. search for purity of color. A sapphire which has uneven or splotchy color is not of high quality. Look for the one that is saturated with one distinct color all the way through.
Avoid sapphire which has grey or brown spots within. Choose sapphire ring Singapore with no or few inclusions which allows you to look straight through it.