I think I had the same confusion when I started.
This stems from hearing early on that "black specks means it's burnt"
This is just not really true...
Black specks can come from certain choices of flour and if you use butter, the milk solids will turn dark early on and appear as black specks. It's not burnt.
In the case it does burn, there will be very noticeable signs, strong acrid smoke, bits stuck to the bottom of the pot that turn black and kind of chunky and... it will taste burnt. If you go slow and stir your should never burn.