Well the coolest star are a dull color would have to be Courtney Love. She's obviously from outerspace and is known for her low body temperatures. The cats also are dull, but sometimes I are tomato sauce.
The color of a star isn't responsible for how hot or cold it is. Neutron stars are black, but way hotter than our son. The hypothetical black dwarf would be the coolest star if one was found, with brown dwarfs (which have been found) being the runners up.
Not only is this question a matter of opinion, it's also broad. By broad, I mean you could be referring to one of two things: -The coolest single Clone, for example, Trooper "Boil." Or... -The coolest type of clone, such as Clone commandos or engineers.
Red stars are the coolest. Blue stars are much hotter than red stars. You may think that blue stars are the coolest because it represents ice, and red stars are the hottest because it represents fire, but that's wrong.
The coolest star is red; then yellow; then blue. Like on a fire, the bottom of the fire is really hot so its blue. In the middle of a fire, its mostly yellow. Then, on top, it has a little flame of red. :p
A main sequence star is NOT a TYPE of star but a period in a stars evolution. Therefore all stars from the hottest to the coolest are on the main sequence at some stage - with the exception of brown dwarfs which do not reach the main sequence.