Toadflax Brocade, Calophasia lunula, would be my hunch, see image here: http://ukmoths.org.uk/show.php?id=672
What do you reckon?
It's not that one. Sorry about not mentioning I live in Maine, USA, it didn't occur to me to add that in the beginning. I caught the caterpillar Tuesday and decided to keep it till it hatches from a cocoon and let it go then. It went into cocoon stage since I asked for ID. The cocoon is pale brown, two centimeters long and one centimeter wide.