For a screwdriver what I want is a spring temper shaft with a harder tip, but not too hard.  This is not a cutting tool where you stop the temper before it even shows.  I like nice solid blue for the tool and brown with purple just for the tip.

It takes about 5 or 6 minutes tickling in and out of the heat and waiting for the color to come, did I mention don't even think of trying to rush it!

When at last you have the color just the way you want it, dunk it. Water is fine here, it won't warp on you at this point.

After the quench, take some fine abrasive paper and sand off the color or at least enough of it so you can see the entire length in bright clear metal again.

I repeat the entire process 3 times in all to get the deep even temper. I know guys do it less, but three times through and you can count on it.

Here is what I want to see. Deep even blue spring temper right to the tip where it fades to purple with just a bit of brown spotting at the very tip.

Works for me!