Mathematica Code to test BoundaryStyle setting of RegionPlot

region_plot_test.nb

hexToRGB = 
 RGBColor @@ (IntegerDigits[#~StringDrop~1~FromDigits~16, 256, 3]/
     255.) &
colors = Table[ColorData[1][x], {x, 0, 36, 1}];
colorsHex = {"#DA96D1", "#DC4AD4", "#97E43B", "#52C858", "#B36EE2", 
   "#B0429C", "#827CE0", "#CC3B4F", "#7BDA91", "#498727", "#E94292", 
   "#C3D676", "#59397F", "#3EC3A3", "#E24925", "#5999EB", "#E69F34", 
   "#506BB4", "#DC722A", "#48BAD3", "#C0D5B7", "#72244C", "#C1B535", 
   "#D77F84", "#557B49", "#642B23", "#C3BCCF", "#D5A974", "#3D3448", 
   "#A95531", "#536B90", "#53817B", "#9B5B87", "#323B24", "#93776C", 
   "#7C6727"};
colors = Table[hexToRGB[colorsHex[[i]]], {i, 1, Length[colorsHex]}]
b = {False, False, False, False, False, False, False, False, False, 
  False, False, False, False, False, False , False, False, 
  aS <= 0 && bP >= 0, aS >= 0 && bP >= 0 }
RegionPlot[b, {aS, -0.5, 1.}, {bP, -1.5, 1.5}, PlotPoints -> 50,
 FrameLabel -> {"S", "P"},
 PlotStyle -> colors,
 BaseStyle -> {FontSize -> 22},
 BoundaryStyle -> Directive[Black, Thick], Mesh -> None]