Thank you! After some research I discovered that if you catch the CTLCOLORSTATIC message, you can change the readonly background color too!
So, if you add something like this to the EditControl:
if .textcolor isnt ""
SetBgndColor(…) will change the background even if the control is read-only! 🙂
Now my problem is that if you use that code, then the readonly background color will always be the same of the not-readonly window…