Different colours top to bottom

We are trying to create a document in InDesign and when ever we create something with colour it appears to be a different shade of the same colour if we drag or copy the object to the bottom of the page (darker at the top) see below for the example.

we have reset prefs & reinstalled... this is happening on more than 1 pc but not all of them.

it's not the monitors as you can see this is a screenshot and it also happens with our remote software.

Thanks

Oscar