plotting solution(x,y,z) and freezing point on the same graph

I would like to plot the melting points of three component mixtures (call them a, b and c) on a plot that also that shows the composition of the mixture. [an example point would be: a=0.8, b=0.1, c=0.1, Tm=20 °C]. I think the best way to do this would be to make a triangle plot sort of like the one shown in the attached figure, but aside from using gizmo (which i don't really think is the correct solution) i have no idea how to go about this. Any suggestions would be very helpful.

One thing I would like to try if I can figure out how to plot the 3-componet mixture is to either color code the freezing point values or make isotherm lines on the plot sort of like a contour map. bz_0.png (416.56 KB) freezing_point.png (419.6 KB)