Polen, Woiwodschaft Podlachien, Bialowiez, Wiese in der Pufferzone des Nationalparks, 160 m, 5. August 2015 (Freilandfoto: Marek Idec)
Colias croceus, Colias erate, and Colias hyale seem very similar to me. As one picture is worth more than a thousand words I attached another picture showing the area where I photographed the buttefly.
I would appreciate any information about this butterfly and why you think this is this particular species. Thanks in advance.