-------------------------------------------
switch variable: $surfcolor -- background color
switch value: 0-4
switch variable: $colscale -- overlay color
switch value: 0-17
-------------------------------------------

Background Color (curvature, sulcus/gyrus)

The radio buttons to the right of "Col:" sets
whether or not to use the .curv data field (which
can be loaded with curvature or sulcus/gyrus) to
modulate the background surface color.

With data overlay off ("ovlay" is unticked,
$overlayflag is 0), the data in the .curv field
is displayed in red and green:

  red: locally concave (or sulcus) => .curv is pos
  green: locally convex (or gyrus) => .curv is neg

If data overlay is turned on ($overlayflag is 1)
and curvature (or sulcus) has been loaded,
curvature or sulcus/gyrus is displayed as two
shades of gray:

  dark gray: locally concave (or sulcus) => .curv is pos
  light gray: locally convex (or gyrus) => .curv is neg

The unlabeled entries further to the right set
the brightness (0-1, default=0.3) and contrast
(0-2, default=1.3) of the grays (numbers below
1.0 reverse contrast of light/dark gray
background color).

Data Overlay ColorScales (real- or complex-valued data)

If data overlay is on ("ovlay" is ticked,
$overlayflag is 1), then there are 17 different
data overlay color scales to choose from.  Seven
are visible on interface (w1, ht, bi, BRy, BR,
lt, fs).  For more colscales, see below.

-------------------------------------------
funct (left-click): make colscale popup
-------------------------------------------

A left-click on "Col:" makes a color scale popup
with more verbose descriptions almost all
available color scales.  R-click help works here,
too.

F3 panel

Displaying area ("ar") and shear ("sh")
distortion as a red/green background color only
works when cortex is being unfolded.
