The experimental math conversion tool for Goodnotes6 is fairly good. It can convert most of 1-liner math handwriting satisfactory!
However, it seems that the color of produced math formula is black only and can't be changed.
Please make it possible to change color of the produced formulas, like other objects such as lines and typed texts. Assuming LaTeX as the conversion backend, it shouldn't be very difficult to make it by inserting a preamble \color{colorname} just before the math script.