Pieris brassicae. This species is very common here and it often gets this yellowish shade. This one, for example, looks almost identical to the one that came to visit you this morning :)Awesome close-up, @valth! :) I am pretty sure it is indeed
http://vithotarek.cz/motyli/motyl-belasek-zelny-pieris-brassicae-184-c.php