@betachka,
I am not sure if you can win but you can ask the buyer to open a return request, saying it was because of the color. you might not have to pay the return shipping. Hopefully, one of the clothing sellers will answer with better information.
Because you are located in Latvia, if the sale was to a person in a different country you will have to decide if paying the buyer for the return shipping is worth it or not. If you use Paypal you will also lose the fees you paid them for the transaction. If the hat was inexpensive it might be better just to issue a refund.
I would always add to a listing with light or pastel colored items that monitors and screens can cause colors to be seen differently, then state that it is (light blue). To help avoid colors looking different in photos, do not photograph items under incandescent light which can add yellow to a color, or under a fluorescent light which adds green to colors. Use a flash if the item is not too reflective or open shade natural light or daylight corrected bulbs.
"THERE IS NO SUCH THING AS FOOLPROOF, BECAUSE FOOLS ARE SO DARNED INGENIOUS!" (unknown)
