Not sure if it is for a Colt or High Standard. If the former, it has no notch for the side button magazine release of the Woodsman 2nd series so it would be for a 3rd, or 1st.
I don't believe that it is a Colt magazine. Everything about it appears to be an early magazine for a Hi Standard HD military. It also seems to be in excellent condition!
Linda, I think you may have a mag for a High Standard U.S.A. H-D or H-D Military. Here's a pic of the latter with its magazine. It's a later one (March 1948); earlier ones may have that long groove on the side. The second pic is of the early style mag with the groove.