This is a very clear image of Ruby posing in his cabana outfit. It's cropped at the bottom so that we can't see his black socks.
When did they finally get him into that cabana outfit? It wasn't right away, and it may have been late in the day. Here he is being taken to Fritz' office at 3:00, and he is wearing his own dress shirt.
Notice that the collar of the shirt is not pressed down as we see in the cabana photo.
So, this is definitely his own shirt.
And then, when they brought him to his first hearing before a judge, he was still in his own shirt.
So, the changing into the cabana clothes must have come late, and it may have been done mainly for the sake of taking pictures. The claim that Ruby was immediately stripped of his clothes on the 5th floor is proven to be a lie.