I think the issue the user above tried to point out but couldn't is that how to decide which checks should be done everytime for every car. Considering DQs due to plank wear are ridiculously rare(I don't think there was a single DQ in the turbo hybrid era due to greater than allowed plank wear before this one. Feel free to correct me I am wrong), it's reasonable for the FIA to not have that as critical element which is required to inspected for every car. Maybe they could select tracks where this could be an issue (like cota, spa, Baku) and only on those weekends either check all the cars or atleast the lead car from each team for plank wear transgressions.

Edit : Regarding your idea for a plank with different colours at different thicknesses, it may be technically feasible but such a manufactured plank will be far more expensive than the current wooden plank(considering 23 races and 20 cars then it's 460 planks a year so costs will add up real fast). I don't think the FIA will spend money on a policing an issue that occurs so rarely. Maybe the new increased driver fines can be used for this purpose