Phase that occurs after a main sequence star?

a red giant

First of all, there cant be a white main-sequence star. White would be a white dwarf, red a giant or super giant. There can be blue, yellow, orange, red and anything in between those i guess. The...

Protostar is an early stage of the Star Cycle. Protostars begin to bring itself together and form a Main Sequence star. Which is the stage our Sun is in. Main Sequence stars are just like our Sun,...

As in a particular star - that's impossible to answer. As to a type of star from it's original formation, an O type star.

Any star that it fusing hydrogen into helium is classed as a main sequence star.