[core] Allow instantiation of TColorNumber from RGB arrays

This allows pass Python tuples to any of the `Set*Color` methods.

core/base/inc/TColor.h

@@ -14,6 +14,7 @@
 
 #include "TNamed.h"
 
+#include <array>
 #include <vector>
 
 class TArrayI;
@@ -140,6 +141,7 @@ class TColorNumber {
 public:
    TColorNumber(Int_t color) : fNumber{color} {}
    TColorNumber(std::string const &color);
+   TColorNumber(std::array<Float_t, 3> rgb);
    Int_t number() const { return fNumber; }
 
 private:

core/base/src/TColor.cxx

@@ -3646,6 +3646,7 @@ void TColor::InvertPalette()
    std::reverse(fgPalette.fArray, fgPalette.fArray + fgPalette.GetSize());
 }
 
+////////////////////////////////////////////////////////////////////////////////
 /// The `color` string argument argument will be evaluated
 /// to get the actual ROOT color number, like `kRed`.
 /// Here is how the string is parsed:
@@ -3681,3 +3682,7 @@ TColorNumber::TColorNumber(std::string const &color)
       throw std::invalid_argument(msg.str());
    }
 }
+
+////////////////////////////////////////////////////////////////////////////////
+/// Instantiate a color from a tuple of RGB values between 0.0 and 1.0.
+TColorNumber::TColorNumber(std::array<Float_t, 3> rgb) : fNumber{TColor::GetColor(rgb[0], rgb[1], rgb[2])} {}