The color of the cement depends on the raw materials used to manufacture it. If the raw materials contain more iron the resulting cement will be darker. Colour has no significance on any properties of the cement. The strength of the cement is dependent only on the proportion of raw materials in the mix.
Blended cements (PPC & PSC) are better cements when compared to OPC cements with respect to DURABILITY OF CONCRETE STRUCTURES. They can be used for all normal construction purposes. Blended cements have certain added features that aid in the durability and longer life of concrete structures.
Advantage of blended cements:
High Early strengths cements have more heat of hydration which affects the concrete quality in the long run unless adequate initial curing procedures is not done at site. Use of Blended cements leads to reduced heat of hydration and hence less micro-cracks if not cured properly during initial stages. Hence use of Blended cements improves durability of the concrete structure.