Although the default speed for a minor highway is likely higher than 35 MPH, after you (and other wazers) drive the road enough, waze will learn that the normal speed really is 35 MPH (presuming that most drivers aren't driving at 50 MPH despite the speed limit) and should then stop showing the road in orange when the traffic is flowing at 35 MPH.
Waze is going to route you the fastest route based on the road speed data that it has. This route doesn't avoid orange roads per se. Rather, the route simply takes into account what the current speed of the road is. Waze frequently routes me on yellow/orange/red marked roads, presumably because the alternatives aren't any faster.
Speed limits are a frequently raised topic. For example see the thread here: viewtopic.php?f=13&t=15057