Unusual looking logon screen

I've found one of my machines has a rather odd problem. Please take a look at the screenshot below and see if you have had similar/ know how it got that way. I'm pretty sure one of the more tech savvy students have done it but if i knew how it may help prevent it again.

As soon as you log on it reverts back to the standard colours so i've been unable to change it by logging in as local admin for example. I've also tried copying a default user profile thinking it may be from there but it isn't. Does anyone know of where the colors for the logon screen are kept in the registry. Short of a solution I can rebuild the machine but as it's going to the big computer room in the sky over the summer i really can't be :censored:.

looks like a high visibility colour scheme. I dont know if that helps you at all
could it be a registry setting?

<edit>

looks like high contrast black

Thats what I thought it was however I've been unable to find the relevent registry key for the logon screen. I've found a default desktop setting for every other user though so I'm pretty sure it's got to be there somewhere.
Was hoping someone else had seen something similar because i would like to prevent any future occurrences as well

We had that its the students pressing alt + Shift + print screen, we have removed by logging as local admin pressing the keys going in to settings and untick high contrast then we copied the admins profile in to the default one.

Yes we have had the same problem. If I remember right it is a keyboard shortcut:

Left ALT+left SHIFT+PRINT SCREEN (Switch High Contrast either on or off)

Disable Sticky Keys and High Contrast - EduGeek.net Wiki gives the way to stop this happening again

That was it thanks. I've been trying to remove accessibility options but I'm sure when I do there will be someone who genuinely needs them. However for anyone else who gets this on the general tab of the accessibility options is a tick box to apply settings to the logon screen :)