From what I know they were aware of the effect of a yellow sun on their physiology, so given how advanced they were why did they not turn their sun yellow (IIRC they had the ability to turn a yellow sun red) or emulate the rays of a yellow sun.

Would they have not preferred the increases in power and ability they would get from doing so? Was this ever touched on in the comics?

I think only jor-el and Zoe-el knew about that.mainly due to the fact that jor-el pre 52 was sent to earth by his father as a right of passage

Pre-52, there were a handful of other Kryptonians who knew about the yellow sun gifting them abilities, but they were part of a small sect of Kryptonians who departed the planet once the government made it illegal for them to go off-world or whatever. One of them was Kristen Wells.

But as already stated, no one on Krypton knew about it.

My thought on the whole situation was Jor-El theorized the effect of Yellow Sun Radiation on Kryptonion Physiology but never informed because he never had a way to prove it or to work on it on top of all the other things he was doing. Also let's face it, if he did, certain kryptonions would have wanted to weaponize it and he would have feared the results.

@Suprman said:

Also let's face it, if he did, certain kryptonions would have wanted to weaponize it and he would have feared the results.

Viltrumites reborn, anyone?

@JonSmith: Actually I was thinking more along the lines of Zod. But he's also my favorite Supes Villain so my mind often strays to him when conquering things and the like.