When that happens to roses, it is because the graft died and the root stock put up a plant. But I know nothing of how raspberries are cultured.

If it were me, I would go back to where I bought them and ask them WTF is going on.

Other possibility - the yellow is a hybrid, seeds dropped, and you get segregation into parents, cousins, etc.

And final possibility is what was stated astutely above - growth from a rootstock if the plants were grafted.

grown from a couple bareroots.
dont think these are seeded plants. these would be the fall canes from last year. only had the one crop from them so far. never known raspberries to come up from seed, but...

but they are ALL purple now.
these are fine tasting, but those yellows were amazing.

there are a few yellow bearing canes so far.
damn. those were so good.

just have a little thing here on the farm about color, and foods that are beautiful as well as delicious. and those yellow ones were both.

and the red ones i planted are insane. i planted 3 quart pots of them on my hugelpile last spring. i guess this thing is a good idea, because i have a 3' thick, 20' long hedge of the things now. i have to pull them out.

The planting bed may have been too"hot" - I might have had too much chicken manure in the mix. Also - the chickens pulled out some of the blackberries. I had to leave for 6 weeks, when I got back there was no sign of the blackberry plants and only some bare sticks with no roots for the raspberries.