How can I invert the colors in a color bar

Question

I have this Mathematica code

Clear[colorbar]
colorbar[{min_, max_}, colorFunction_: Automatic, divs_: 150] := 
  DensityPlot[y, {x, 0, 0.1}, {y, min, max}, AspectRatio -> 10, 
  PlotRangePadding -> 0, PlotPoints -> {2, divs}, MaxRecursion -> 0, 
  Frame -> True, 
  FrameLabel -> {{None, Subscript["R", "min"]}, {None, None}}, 
  LabelStyle -> Directive[FontFamily -> "Helvetica", 17], 
  FrameTicks -> {{None, All}, {None, None}}, 
  FrameTicksStyle -> Directive[FontFamily -> "Helvetica", 15, Plain], 
  ColorFunction -> colorFunction]

Mn = 250; cn = 0.25;
Md = 7000; b = 6; a = 3; h = 0.2;
υ0 = 20; β = 1.5; ch = 8.5;
Lz = 10;
E0 = 600;

Vn = -Mn/Sqrt[R^2 + z^2 + cn^2];
Vd = -Md/Sqrt[b^2 + R^2 + (a + Sqrt[h^2 + z^2])^2];
Vh = υ0^2/2 Log[R^2 + β*z^2 + ch^2];
Vt = Vn + Vd + Vh;
Veff = Vt + Lz^2/(2*R^2);

f[R_, pR_] := 1/2*pR^2 + Veff /. {z -> 0};

plrange = {{0, 13.5}, {0, 47}};
valrange = {0, 6};

C0 = 
  ContourPlot[Evaluate[f[R, pR]], {R, 0.001, 15}, {pR, 0, 50}, 
    Contours -> {E0}, ContourStyle -> {{Black, Thickness[0.005]}}, 
    AspectRatio -> 1, ContourShading -> False, PlotPoints -> 200, 
    PerformanceGoal -> "Speed", PlotRange -> plrange];

With[{opts = {ImageSize -> {Automatic, 550}}, cf = "Rainbow"}, 
  Row[{Show[
    ListPlot[List /@ data[[All, {1, 2}]], 
      PlotStyle -> ({PointSize[0.01], ColorData[cf][1 - #]} & /@ 
        Rescale[data[[All, 3]], valrange]),
      PlotRange -> plrange, 
      AspectRatio -> 1, Frame -> True, RotateLabel -> False, 
      Axes -> None, FrameTicks -> True, 
      FrameLabel -> {"R", OverDot["R"]}, 
      LabelStyle -> Directive[FontFamily -> "Helvetica", 17], 
      ImagePadding -> {{60, 20}, {60, 20}}, opts],
    C0], 
    Show[colorbar[valrange, cf], 
     ImagePadding -> {{20, 60}, {60, 20}}, opts]}]]

I inverted the "Rainbow" color scheme using

{..., ColorData[cf][1 - #]}&

and produced the following nice plot.

However, I can't find a way to invert the colors in the color bar. To be more specific, according to my data red should correspond to 0 of Rmin and deep purple to 6. I hope it is easy to invert the order of the colors in the color bar. Can someone tell me how?

Answer 1

Show[Replace[
  colorbar[valrange, cf], (VertexColors -> x_) :>  VertexColors -> Reverse@x, Infinity], 
 ImagePadding -> {{20, 60}, {60, 20}}]

Answer 2

The last solution is a bit too long for my taste. Here's something more compact:

colorbar[{0, 6}, ColorData[{"Rainbow", "Reverse"}]]

This also works for most of the other named color schemes:

colorbar[{0, 6}, ColorData[{"TemperatureMap", "Reverse"}]]