My reference materials are in the basement and I am not so I grabbed a chart like yours for convenience. If you can consistently see the light yellows you have better eyes than I do. I usually don;t see a change until over 400 and then colors are changing quickly even with indirect heating.And blue has always been spring temper though there is an area of "blue embrittlement" to avoid. But I can tell you from experience that with typical soft solder fluxes you start having problems getting them to work right when you get into the yellows. For smaller parts I prefer my big soldering gun or indirect heating. It's too hard to control the heat with a flame. Even with more massive parts you have to be careful and keep the flame moving. That's with soft solder. In that respect brazing is easier. But note, even Dunlop admitted he couldn't control heat carefully enough to silver solder a front sight without scaling an unprotected bore.
So I use the solder to test the temperature while heating carefully and stop when the solder flows well enough to make a nice fillet. That's all you really need to know besides cleanliness and choosing the right flux. The rest is practice. (You know this but maybe someone reading this doesn't.)
