Christie,
they'll start turning yellow, and the rind/skin will begin to shrivel somewhat when they're ripe. I've got P.incarnata climbing up in a little bur oak in the front yard - haven't looked all that closely, but I don't think any of the fruits on mine are ripe yet.

Thanks - I think these got broken off a little early then. The vine was low to the ground and a rabbit could've reached them. I've been trying to watch them so they won't all get eaten before we get a chance to sample them. They are growing up through a viburnum trilobum and there are a couple dozen golf ball sized fruits and some very small ones too. I'm guessing the little ones won't have time to ripen since the bigger ones are taking so long.
Lucky - My little bur oak has put out a lot of new growth in the last month or so. I think it's nearly four feet tall now. The top two feet of the trunk is green because it's this years growth and most of that has been very recently. I was surprised how much it shot up this late in the season. The pin oak that it's replacing is almost leafless already so it's a good thing that the bur oak is a fast grower. Stupid pin oak has been near death for 15 years now and I think each year will be its last.