Fans going to catch a showing of "Wicked" bitter ditch the green face paint ... 'cause that's a no-no for one major theater chain ... and it'll need to be washed off. Here's the deal -- since "Wicked" opened over the weekend ... a few videos have been posted to social media from fans who had to wash off their green face paint if they wanted to be admitted into an AMC location. The issue is not a matter of AMC hating on Elphaba fans ... it's just a dress code rule that has been in place for a while -- namely, no face coverings, which include face paint. A source with knowledge tells TMZ there has been no issue with customers complaining about the rule or that they may have been asked to wash off the green. As we previously reported ... there has been no shortage of fans going in cosplay to see the musical -- which had a massive weekend opening. So far ... Wicked has swept up $114 million in North America and an additional $50.2 million internationally ... bringing the flick's global bag to $165 million. That number number is sky to keep flying skyward over the Thanksgiving holiday weekend ... fans just need to remember to leave the face paint at home.