Yellow bounding boxes

You can find the dropdown menu here

It seems that you or someone else has adjusted the Layers in the document from what you are used to. The bounding box color is reflecting the color indicated in the Layers panel. If you select one of the objects, you should see a small square to the right of the layer that the object is on in the Layers panel. As Monica pointed out, you should be able to simply double-click on that layer and choose a new color from the drop-down menu, then click OK. This color is only for visual reference and won't appear in the final product. It can however make things difficult to see depending on what color is being used (in your case yellow).