Not sure I agree with this....the (admittedly few) supernovae I have seen looked fairly unique, though the coloration was much the same. I think that's a matter of the physics involved and the composition of the supernova (mostly hydrogen). Colored novae are more the result of the energy from the neutron star or pulsar at the nova's center exciting/energizing the matter in the expanding clouds of gas surrounding them.
Ok I agree except for the hydrogen part because that's incorrect but I wont waste time explaining it instead I will take about the game,
First of all Supernovas are never always the same color, look at a nebula, now look at a different one, they will never look the same, but in this game they always look like clouds with the same color and same feel, Yeah sure some Supernovas in this game can end up doing a different cloud-ish explosion look but the colors never change, Supernovas almost always have a different color to them, depending on the mass of the star and if it will form into a Blackhole or a pulsar, I mean I'm not forcing Dan or whoever is the physics/art designer to change the Supernovas but it would definitely be cool for them to change the mechanics