[Freesurfer] Color scale in TkSurfer

I'm plotting potential distributions on a cortical surface using TkSurfer. The color scale "Heat" gives the most comprehensible plots. However, I would like to have the maximum values to be plotted in red instead of yellow, and minimum in dark blue instead of light blue.

max +threshold 0 -threshold min -> Overlay values yellow red gray dark blue light blue -> Heat colorscale red yellow gray light blue dark blue -> Desired colorscale

Is there a way to have the color scale like this? I tried the color scales 'green red' and 'blue red', however, when I select these scales the brain surface disappears.

Thank you, Zeynep.