feat: color: add channel properties to color

Add extra properties to the `color` type.
- `red`
- `green`
- `blue`
- `alpha`

internal/compiler/generator/cpp.rs

@@ -3048,6 +3048,9 @@ fn compile_builtin_function_call(
             ctx.generator_state.conditional_includes.cstdlib.set(true);
             format!("[](const auto &a){{ auto e1 = std::end(a); auto e2 = const_cast<char*>(e1); auto r = std::strtod(std::begin(a), &e2); return e1 == e2 ? r : 0; }}({})", a.next().unwrap())
         }
+        BuiltinFunction::ColorRgbaStruct => {
+            format!("{}.to_argb_u8()", a.next().unwrap())
+        }
         BuiltinFunction::ColorBrighter => {
             format!("{}.brighter({})", a.next().unwrap(), a.next().unwrap())
         }