Generally with boas, darker. The greys ('baby greys') along the side will usually fade and then cream background color will turn tan or brown. Yellow is the last pigment to develop in boas and it comes in over the first few years turning them tan/brown.
99% of the time, if the strain isn't identified then that means it's kahl aka original strain. Sharps usually go for more and aren't quite as common still. In the past it was always default that if no strain was mentioned, it's kahl. If it's sharp, it's called out aka sharp albino aka sharp sunglow etc
Perhaps it's changed a bit over the years and you are correct, it's always good to be cautious and get actual verifiable information from the seller.