I've got some wood shafts I just dipped in an oil-based poly (Minwax polyurethane), and I was wondering...if I do a white cap on the back ends, will an overcoat of poly mess with the white color. This stuff seems amber in color, so I was just wondering?

I must be insensitive. I use the stuff all the time and never noticed a yellow cast to a white cap. I think spar urethane is supposed to do that, but I use both the water-based and oil-based wipe-on polys and don't see a prob.

A warm glow beats stark white anyway.
Killdeer  

Well, I haven't added the cap yet...just curious, Killdeer. Thanks...

As a professional painter, I would say yes it will yellow. Anything that is oil based will yellow. How noticeable it will be depends on the color it is over. White being the worst. Generally the yellowing occurs gradually so that you don't notice it, but if you lay something pure white up against it you will definiely see it. I have rooms that I have glazed with oil based glazing liquid and you would never notice the yellowing until you took a painting off the wall. The water based polys out there are very good and stay clear. They are tough. I just refinished some hardwood floors with some and they look great and I expect them to hold up well. Good luck with your woodies Chris.
Brian

Even if you capped them with oil based white paint they will yellow.

Some excellent advice Brian. Now, don't get me wrong, I love water-based poly. Goes on smooth, easy to clean up, and best of all, almost no smell. But I recently had the chance to test the two kinds of poly by coating two dowels with each and leaving them in a snow bank for a few months. I have to say, the oil-based came out in much better condition. Which makes me wonder: could I just do a base layer of oil-based (especially seeing as it's already on there), cap and crest, and then do an over coat of water-based poly? Just curious...

There is no doubt that oil is more durable. You would have had to put on three coats of water based to 2 coats of oil. I think that even though the oil based one lasted longer, the water based one would have out lasted the life of the arrow.You can put the water based over the cap and crest. What's important is the paint going over the oil based poly. What you should do is put a thin coat of oil based primer over the oil based poly and then you can use water based paint and whatever poly you want.

Why, put anything on the cap dip? The cap dip by itself is all that's needed, anything on top of that is just over kill. Just put the clear up to the end of the cap dip.
Bob

I'm with Bob. I crown dip and crest and then dip the point end to just past the crest to give it some protection. Hap

putting the water borne poly over oil poly will yellow also-if your really worried about sealing-try car wax [after fletching]