Question
What is happening my yellow straight neck squash are turning green.

Answer
This is not unusual with certain varieties. The variety I am currently growing starts off green and then fades to the point that the squash has green stripes, which then slowly fade away until the entire squash is yellow.

One thing you may want to monitor to ensure the change occurs more quickly is to limit the amount of nitrogen applied to the plant. Fruit-bearing plants require higher amounts of phosphorus and potassium for larger growth, a more abundant harvest, and good coloring. But regardless, the squash will eventually turn yellow when ripe.

I hope this answered your question. Please write again if I can ever be of assistance.

Regards,

Mike