SalesOrderDetail table AdventureWorks2008R2 Primary Keys

Question

Hello,

I am working through the Beginning Microsoft® SQL Server® 2008 Programming text.  I have an understanding a table can have only one primary key.  However, it appear the SalesOrderDetail table has two: the SalesOrderID and the SalesOrderDetailID.  Below is a screen shot of the table columns.
I recognize the SalesOrderID is a is a foreign key to the SalesOrderHeader table.  However, it appears, by the coloring of the key and the PK in (PK, FK, int, not null) , that it is also a primary key for this table.  Can someone help me understand this?  Is it that the PK in the column definition refers to the fact it is a primary key in another table?  If so, why is it gold colored in this table?

Thanks