What you are seeing is just some striation and variation in the base glass. It is totally common. It's just more noticeable on some marbles than others. Making machine made marbles is not a precision process - not even close. The way the glasses mix in the tank, the crucibles or the stream can vary from minute to minute. What is remarkable is that there is any consistency at all.
In your marbles, there is lots of variation in the glass. The base glass on some is nearly clear, others are translucent, some have lots of white filaments, some don't. The amount of striping glass varies from marble to marble too. Variation in marbles is the rule not an exception. But they all still look like Peltier Rainbos, right?