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...
Polaris - the current North star is a multiple star system. The main star Alpha Ursae Minoris is a bright or a possible supergiant with a spectral class of F7. So it's a main sequence star. It's...
Generally a blue star is on the main sequence. However, the colour of a star is related to its temperature. It's temperature is related to the mass of the star - the higher the mass (Size) the hotter...