Show a product field programmatically
Here's how you create a term reference field to a CONTENT_TYPE:


Create a taxonomy vocabulary called, say, "Color" at admin/structure/taxonomy/add.
On admin/structure/taxonomy, click "add term" next to your new vocabulary.
Add terms, such as, say, "blue", "red", etc.
Go to /admin/structure/types/manage/CONTENT_TYPE/fields 
Add a new field called, say, "Color", and, set its "field type" to "term reference". Select an appropriate widget, such as "select list".
Go to /admin/structure/types/manage/CONTENT_TYPE/display and set the field's display to, say, "link". You can try different display options, such as "plain text" too.


Hope that helps.

Appendix:

To create a node and save this field programmatically, follow this example, which has instructions for saving term reference fields.