You've got a few mistakes...Value should be rawValue for RadioButtonList.
There should only be 1 equals signs for the color assignment statements. "=" assigns a value, "==" tests a value.
And then it's always a good idea to put in the curly braces, althought I think for single statements it will work without them.
If (RadioButtonList.rawValue == "Accept") {
TextAccept.border.fill.color.value = "255,255,0";
}
else {
TextDoNotAccept.border.fill.color.value = "255,255,0";
}