I'm looking for a pant that can be worn under waders during the warmer months (and still be effective standing in cold water)

I don't care if it's lightweight fleece or any other synthetic fiber as long as it would be effective with breathable waders.

(By pant, I mean something that is not compression fit - something you could wear into a store or cafe for example. Color is not important - but it must have a left rear pocket and either belt loops or integrated belt - not a drawstring).

I have a pair for colder weather that I picked up at Cabelas and love - but they will be too warm when the temps get above 80.

Any recommendations?