Until you provide more detailed information, there really isn't anything that any of us are going to be able to add
We need test results, not colors (we have no idea what brand test kits you are using)
Salinity
Other tank inhabitants? Are they acting normal?
Recent additions / changes to the stocking list?
Recent additions / changes to the setup?
We NEED more information before we can even begin to theorize on what killed your fish. And even WITH all that information we may not be able to determine the cause