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variable: $meshb -- mesh/label/annot blue (0-255)
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default: 255

The "b" (blue) entry next to the "MESH" button
has seven uses:

 1) sets blue component (0-255) of polygon mesh
    color (display/hide with MESH).

 2) sets blue component (0-255) of next label
    that is displayed using the "D" button on the
    "label:" line.  Changes do not affect color
    of already-displayed labels.

 3) sets blue component (0-255) of the next
    display of vertex points (toggle point
    visibility with middle-click MESH butt).

 4) sets blue component (0-255) of the next
    display of annotation border dots
    ($annotborddotflag on LABEL CONTROLS popup).

 5) sets blue component (0-255) of the next
    display of coordinate isocontours (lower
    middle "isocont" tickbox).

 6) reports blue component of MGH annotation
    label color at currently clicked vertex
    (if MGH annotation loaded)

 7) sets blue component of MGH annotation
    label color used to extract underlying
    .val(.val2) vertex data
