fix(Color): make constructor idempotent

Problem:  passing a `Color` instance to the main constructor of `Color`
          (i.e. `Color.new()` or `Color()`) silently causes a bug and
          does not throw an error

Solution: immediately return the argument back to the caller when passed
          a `Color` instance, thereby making the constructor idempotent

CHANGELOG.md

@@ -6,6 +6,16 @@ The format is based on [Keep a Changelog], and this project adheres to [Semantic
 
 ## [unreleased]
 
+### What's New?
+
+-  Added static/class function `Color.is_Color()` for detecting Color instances
+
+### Changes
+
+### Issues Fix
+
+-  Made `Color()` constructor idempotent (previously, passing a `Color` inst silently caused a bug)
+
 ## [v1.1.0] - 23 July 2024
 
 ### Highlight Groups

lua/github-theme/lib/color.lua

@@ -109,6 +109,10 @@ local M = setmetatable(Color --[[@as GhTheme.Color.Static]], {
 ---@return GhTheme.Color
 ---@nodiscard
 function M.new(color)
+  if M.is_Color(color) then
+    return color --[[@as GhTheme.Color]]
+  end
+
   local ty = type(color)
 
   if ty == 'string' or ty == 'number' then

test/github-theme/color_spec.lua

@@ -51,6 +51,13 @@ describe('Color', function()
         assert.are.same(ex.str, c:to_css())
       end)
 
+      it('should construct from an integer', function()
+        local n = 0x12345630
+        local c = Color.from_hex(n)
+        assert.are.same(n, c:to_hex(true))
+        assert.are.same('#12345630', c:to_css(true))
+      end)
+
       it('should error when given invalid args', function()
         assert.does.match.error(function()
           ---@diagnostic disable-next-line: param-type-mismatch
@@ -99,6 +106,13 @@ describe('Color', function()
       assert.are.same(ex.str, c:to_css())
     end)
 
+    it('should construct from an integer', function()
+      local n = 0x12345630
+      local c = Color(n)
+      assert.are.same(n, c:to_hex(true))
+      assert.are.same('#12345630', c:to_css(true))
+    end)
+
     it('should infer from rgba components', function()
       local c = Color(Color.from_hex(ex.str):to_rgba())
       assert.are.same(ex.hex, c:to_hex())
@@ -116,6 +130,21 @@ describe('Color', function()
       -- assert.are.same(ex.hex, c:to_hex())
       assert.are.same(ex.str, c:to_css())
     end)
+
+    it('should be idempotent', function()
+      local orig = Color(ex.rgba)
+      orig.alpha = 0.5
+      local new = Color(orig --[[@as any]])
+
+      for _, c in ipairs({ orig, new }) do
+        for _, k in ipairs({ 'WHITE', 'BLACK', 'BG' }) do
+          rawset(c, k, c[k])
+        end
+      end
+
+      assert.are.same(orig, new)
+      assert.are.same(orig:to_css(true), new:to_css(true))
+    end)
   end)
 
   describe('conversion', function()