When IE8 is set to Document Mode of IE7, dragging and dropping portlets, the entire screen can turn red. This is most likely due to opacity handling.
This issue can be intermittent, but here is the most consistent way to reproduce:
1. Startup Liferay (I was using Trunk Rev127035)
2. Before going to Liferay, set IE8 to be in Browser Mode: IE8, Document Mode: IE7
3. Create a new page called "test"
4. Under the "Add" Menu, click More
5. Drag 1 portlet into a column (valid dropzone). (You'll see the blue placeholder.)
6. Drag another portlet somewhere other than a valid dropzone. Be sure to not drag over any valid dropzones (columns). If the blue placeholder displays, you'll need to refresh the page and start again at Step 4.
7. Once you've let go of the mouse. Hover over a valid dropzone. The blue line will now display. Click the mouse to "drop" the portlet.
8. Attempt to drag another portlet. You'll get a red & orange screen as shown in the screenshot.