I bought 2 cucumber plants and they were labeled as the same type of plant. I put tomato cages around them so that I could find the cukes easier. One of the plants is growing yellow cukes that have brown on them. I picked one and cut it and it smells and tastes like a cucumber but the skin is really tough. I also have a "volunteer" crook neck yellow squash plant growing very near to it and found a lime green squash on it. Is it possible that these are cross "breeding" or something? That's what everyone at work is saying, but I've never heard of that. The squash plant came out of nowhere because the ones I planted are quite a bit away.
KayB. Is the yellow cucumber round rather than long? If so, it could be a lemon cuke. An old heirloom varity. I don't think that squash and cucumbers will cross polinate. I am pretty sure thay won't cross the first generation. Strange things happen in the plant world. Sounds interesting enough that you might check with OSU. Save the seeds.