I read some time ago that if polyurethane or marine spar is applied over white or yellow paint, that it will leave a blotchy appearance. I wonder why that is. And I wonder why this doesn't happen when applied over dark colors.
I have some very old dining chairs that I'm going to paint a medium shade of green and then apply marine spar over the paint. There will be used outdoors to hold flower pots. The reason for the marine spar is that I would like to get more than one year out of the paint job, but I don't want a blotchy appearance either.
Any thoughts or suggestions would be appreciated.