Reversing the ColorScheme used in an ArrayPlot and setting the font size in the color bar

Question

I have a matrix of data that I am plotting via ArrayPlot.

FData = {{0., 0., 0.066812, 0., 0., 0., 0.}, {0., 0.479787, 0., 
   0.0683112, 0., 0., 0.}, {0.0669646, 0., 0.0697005, 0., 0., 0., 
   0.}, {0., 0.0683715, 0., 0., 0., 0., 0.}, {0., 0., 0., 0., 0., 0., 
   0.}, {0., 0., 0., 0., 0., 0., 0.}, {0., 0., 0., 0., 0., 0., 0.}}

I would like to reverse the color bar colors in the Plot legend. I used:

ArrayPlot[
 FData,
 PlotLegends -> 
  BarLegend[{GrayLevel, {0, Max[FData]}}, 
   LabelStyle -> {FontSize -> 20}], DataReversed -> False]

And this gives me:

The colors are flipped in this figure and I'd like the darkest to represent the highest number in my matrix.

When I try to "Reverse" my data (which doesn't seem sound to me) using the below snippet:

FData[[1 ;; 7, 1 ;; 7]]
ArrayPlot[
 FData[[1 ;; 7, 1 ;; 7]],
 PlotLegends -> 
  BarLegend[{GrayLevel, {0, Reverse[FData[[1 ;; 7, 1 ;; 7]]]}}, 
   LabelStyle -> {FontSize -> 20}], DataReversed -> False]

And that gives me nothing!

Edit/Errata

I have been using PlotLegends -> BarLegend[{GrayLevel, {0, 1}}, LabelStyle -> {FontSize -> 20}] to set the font size. Based on the answers below, how can I go about changing the font size?

I know this is very basic but I can't quite figure out whats going on!

Answer 1

With[{g = GrayLevel[1 - #] &},
       ArrayPlot[FData, ColorFunction -> g, PlotLegends -> BarLegend[{g, {Min@FData, Max@FData}}, 
                 LabelStyle -> Directive[Blue, Large]]]]

Answer 2

With ColorFunctionScaling -> True (default), the data values are rescaled to between 0 and 1, which is then input to the ColorFunction. So the general solution to "reverse" the color scheme is to simply input 1 - x, where x is the rescaled data point, as shown in belisarius' answer.

If you're using a built-in color scheme, you can use the "Reverse" property to automatically reverse the colors as in the following example:

With[{data = RandomReal[1, {10, 10}]},
    {ArrayPlot[data, ColorFunction -> "Temperature", PlotLabel -> "Original"], 
     ArrayPlot[data, ColorFunction -> ColorData[{"Temperature", "Reverse"}], 
        PlotLabel -> "Reversed"]
    } // GraphicsRow
]

---

The documentation for the *Legend functions fully specify how to use the options to style them. Here's an example:

ArrayPlot[RandomReal[1,{10, 10}], ColorFunction -> ColorData[{"Temperature", "Reverse"}], 
    PlotLegends -> BarLegend[{ColorData[{"Temperature", "Reverse"}], {0, 1}}, 
        LabelStyle -> Directive[FontFamily -> "Palatino", FontSize -> 14, Red], 
        LegendLabel -> "Colorbar", LegendFunction -> "Panel"
    ]
]