Correction: the sun is white. The atmosphere refracts the sun's light making it appear yellow to us on Earth. That is why the sky changes colour when the sun sets. http://solar-center.stanford.edu/SID/activities/GreenSun.html
I looked it up because I wasn't sure but Soleil being a capital is not a mistake! Apparently, the names for earth, sun, moon and other planets are capitalized in French.