@Septases Your code works with 'YlGnBu':
I have a different Plotly version, 5.24.0, but it doesn’t matter, because since the initial definition of
ff.create_ternary_contour, in 2021, it always worked with any colorscale in this list:
PLOTLY_SCALES=['Greys', 'YlGnBu', 'Greens', 'YlOrRd', 'Bluered', 'RdBu', 'Reds', 'Blues', 'Picnic', 'Rainbow', 'Portland', 'Jet', 'Hot', 'Blackbody', 'Earth', 'Electric', 'Viridis', 'Cividis']
and the code for ff.create_ternary_contour is unchanged
See https://github.com/plotly/plotly.py/blob/master/packages/python/plotly/plotly/figure_factory/_ternary_contour.py#L241.
update: to answer your second question I searched the forum for this answer:
https://community.plotly.com/t/latexify-ternary-countour-plot-colobar/64470/6. It illustrates how difficult is to update a ternary_contour because such a figure with n contours contains n+3 traces, as it is explained at the above link. If you understand that explanation, then you can try to update correspondigly the n traces with new tooltips.