I have seen that often, too. Older books on smithing in particular will tell you that "blue" temper colors fall into the 600 degree range and are too soft for most knives. In my experience, temper color means less than that. Things like blade finish, and residual grease (even fingerprints) can cause uneven or darker colors than you'd think for the tempering temperature. I temper at 450 on some knives and often see blue. That's in an oven in which I keep an additional thermometer to check the actual temperature. I find most ovens are a bit off, and some more than a bit. It would be worth preheating your oven until the temperature stabilizes, then seeing what the actual temperature is inside. After doing this a few times, you get a feel for how your particular oven should be controlled.
Edited to add: A quick word about your quenching. Since you are using 01, and file steel, which if you are lucky is W-series or 1095 high carbon, you'll want to achieve nonmagnetic, then just a little higher. If you can discern a slight color change hotter than Curie (non-magnetic) it's probably enough. Or, a few seconds more in the forge (if that's what you're using.) You want about 50-75 more degrees. If you are going to use motor oil, at least pre-heat it to 120-130 degrees first- it makes a big difference. I made a lot of knives this way. Better than motor oil would be canola, also preheated, or soybean oil . Better yet would be an engineered quenching oil of the right speed for your chosen steel.
