Here's what i do to heat the banger for dabs. Not sure what the heat/color ratio is for glass/ceramic but i usually heat the banger till the bottom is red hot and glowing, then get the dab ready while the banger is cooling. As soon as the color is gone from the banger ill touch my dab down inside.
I like my dabs on the hot side but you should be able to play with timing the color change for your specific needs. Basically heat the banger to the same temp each time then let it cool to the temp you imagine.