Fix bug concerning assigning colour codes to spectrogram types

Issue #332 There was a limited number of colours to use as tags for different spectrogram types. By adding two new spectrograms, there was an insufficient number of colours. Changed the colour palette.

src/Acoustics.Shared/ColorScales/Palette.cs

@@ -16,6 +16,6 @@ public class Palette
 
         public List<Color[]> Colors { get; internal set; }
 
-        public Color[] ForClassCount(int classCount) => this.Colors.FirstOrDefault(x => x.Length == classCount);
+        public Color[] ForClassCount(int classCount) => this.Colors.FirstOrDefault(x => x.Length >= classCount);
     }
 }

src/AnalysisPrograms/SpectrogramGenerator/SpectrogramGenerator.Core.cs

@@ -29,7 +29,7 @@ static SpectrogramGenerator()
         {
             var values = (SpectrogramImageType[])Enum.GetValues(typeof(SpectrogramImageType));
             ImageTags = values
-                .Zip(ColorBrewer.Qualitative.Dark.ForClassCount(values.Length))
+                .Zip(ColorBrewer.Qualitative.Set1.ForClassCount(values.Length))
                 .ToImmutableDictionary(x => x.First, x => x.Second);
         }
 
@@ -75,6 +75,7 @@ public static AudioToSonogramResult GenerateSpectrogramImages(
             // EXTRACT ENVELOPE and SPECTROGRAM FROM RECORDING SEGMENT
             var dspOutput1 = DSP_Frames.ExtractEnvelopeAndFfts(recordingSegment, frameSize, frameStep);
 
+            // This constructor initalises default values for Melscale and Mfcc spectrograms and other parameters.
             var sonoConfig = new SonogramConfig()
             {
                 epsilon = recordingSegment.Epsilon,
@@ -191,6 +192,7 @@ public static AudioToSonogramResult GenerateSpectrogramImages(
             }
 
             // IMAGE 6) Mel-frequency Spectrogram
+            // The default spectrogram has 64 frequency bands.
             if (@do.Contains(MelScaleSpectrogram))
             {
                 images.Add(