How can I prepopulate a field when creating a new node with the values from a field collection? I am creating an inventory management system in drupal. I have two different content types: and item and a purchase order. 

An item has a name, style code, Colors (this is a field collection with a color name and color code), and a range of sizes (3 to 15 for shoes and XS to 4XL for shirts). Some items don't have colors and some don't have sizes.

In a purchase order, there is a purchase order number and any number of items ordered (a field collection with an entity reference to the item, a field for the number of items ordered, and field for the number of items received). Each item ordered will have one color (one of the colors that the item is available in) and any number of the sizes that was selected in the given item.

My question is how I can populate the color selection (probably a dropdown) with the colors that are in the field collection of the selected item (entity reference). I would also need to populate the sizes list with the sizes that were selected from the item, as well.

I am still pretty new to drupal, and I realize that I may be going about it the wrong way or that I may not have explained everything that someone would need to know to help me. But I am open to new ideas or different solutions. I haven't done much module development, but I would be willing to learn if needed.
You can try and look at this module. It allows to have corresponding node references and hence if you select something from one node, you can prepopulate the other node as well. http://drupal.org/project/cnr