Consistently use "palette spec" not "color spec"

Fixes #1436

man/rgbgfx.1

@@ -14,7 +14,7 @@
 .Op Fl v Op Fl v No ...
 .Op Fl a Ar attrmap | Fl A
 .Op Fl b Ar base_ids
-.Op Fl c Ar color_spec
+.Op Fl c Ar pal_spec
 .Op Fl d Ar depth
 .Op Fl L Ar slice
 .Op Fl N Ar nb_tiles
@@ -111,16 +111,16 @@ Both default to 0.
 When generating palettes, use a color curve mimicking the Game Boy Color's screen.
 The resulting colors may look closer to the input image's
 .Sy on hardware and accurate emulators .
-.It Fl c Ar color_spec , Fl \-colors Ar color_spec
+.It Fl c Ar pal_spec , Fl \-colors Ar pal_spec
 Use the specified color palettes instead of having
 .Nm
 automatically determine some.
-.Ar color_spec
+.Ar pal_spec
 can be one of the following:
 .Bl -tag -width Ds
 .It Sy inline palette spec
 If
-.Ar color_spec
+.Ar pal_spec
 begins with a hash character
 .Ql # ,
 it is treated as an inline palette specification.
@@ -139,7 +139,7 @@ See
 for an example of an inline palette specification.
 .It Sy embedded palette spec
 If
-.Ar color_spec
+.Ar pal_spec
 is the case-insensitive word
 .Cm embedded ,
 then the first four colors of the input PNG's embedded palette are used.
@@ -147,7 +147,7 @@ It is an error if the PNG is not indexed, or if colors other than these 4 are us
 .Pq This is different from the default behavior of indexed PNGs, as then unused entries in the embedded palette are ignored, whereas they are not with Fl c Cm embedded .
 .It Sy external palette spec
 Otherwise,
-.Ar color_spec
+.Ar pal_spec
 is assumed to be an external palette specification.
 The expected format is
 .Ql format:path ,