diff --git a/src/args.rs b/src/args.rs
index 4b89235..9df8016 100644
--- a/src/args.rs
+++ b/src/args.rs
@@ -32,6 +32,10 @@ impl CallArgs {
     pub fn get(&self, val: &str) -> Option<&Value> {
         self.0.get(val)
     }
+
+    pub fn len(&self) -> usize {
+        self.0.len()
+    }
 }
 
 pub(crate) fn eat_func_args<I: Iterator<Item = Token>>(
diff --git a/src/builtin/color.rs b/src/builtin/color.rs
index ec93262..4ab295b 100644
--- a/src/builtin/color.rs
+++ b/src/builtin/color.rs
@@ -36,8 +36,49 @@ pub(crate) fn register(f: &mut BTreeMap<String, Builtin>) {
         }
     });
     decl!(f "rgba", |args, _| {
-        let channels = args.get("channels").unwrap_or(&Value::Null);
-        if channels.is_null() {
+
+        if args.len() == 1 {
+            let mut channels = match arg!(args, 0, "channels").eval() {
+                Value::List(v, _) => v,
+                _ => todo!("missing element $green")
+            };
+
+            assert_eq!(channels.len(), 3usize);
+
+            let blue = match channels.pop() {
+                Some(Value::Dimension(n, Unit::None)) => n,
+                Some(Value::Dimension(n, Unit::Percent)) => n / Number::from(100),
+                _ => todo!("$blue: ___ is not a color")
+            };
+
+            let green = match channels.pop() {
+                Some(Value::Dimension(n, Unit::None)) => n,
+                Some(Value::Dimension(n, Unit::Percent)) => n / Number::from(100),
+                _ => todo!("$green: ___ is not a color")
+            };
+
+            let red = match channels.pop() {
+                Some(Value::Dimension(n, Unit::None)) => n,
+                Some(Value::Dimension(n, Unit::Percent)) => n / Number::from(100),
+                _ => todo!("$red: ___ is not a color")
+            };
+
+            let color = Color::from_rgba(red, green, blue, Number::from(1));
+
+            Some(Value::Color(color))
+
+        } else if args.len() == 2 {
+            let color = match arg!(args, 0, "color").eval() {
+                Value::Color(c) => c,
+                _ => todo!("expected color")
+            };
+            let alpha = match arg!(args, 1, "alpha").eval() {
+                Value::Dimension(n, Unit::None) => n,
+                Value::Dimension(n, Unit::Percent) => n / Number::from(100),
+                _ => todo!("expected either unitless or % number for alpha"),
+            };
+            Some(Value::Color(color.with_alpha(alpha)))
+        } else {
             let red = match arg!(args, 0, "red").eval() {
                 Value::Dimension(n, Unit::None) => n,
                 Value::Dimension(n, Unit::Percent) => (n / Number::from(100)) * Number::from(255),
@@ -59,8 +100,6 @@ pub(crate) fn register(f: &mut BTreeMap<String, Builtin>) {
                 _ => todo!("expected either unitless or % number for alpha"),
             };
             Some(Value::Color(Color::from_rgba(red, green, blue, alpha)))
-        } else {
-            todo!("channels variable in `rgba`")
         }
     });
     decl!(f "hsl", |args, _| {
diff --git a/src/color/mod.rs b/src/color/mod.rs
index 9c155e9..29dac18 100644
--- a/src/color/mod.rs
+++ b/src/color/mod.rs
@@ -171,6 +171,10 @@ impl Color {
         self.alpha.clone()
     }
 
+    pub fn with_alpha(self, alpha: Number) -> Self {
+        Color::from_rgba(self.red, self.green, self.blue, alpha)
+    }
+
     /// Makes a color more opaque.
     /// Takes a color and a number between 0 and 1,
     /// and returns a color with the opacity increased by that amount.
diff --git a/src/selector.rs b/src/selector.rs
index 36d537e..04e704f 100644
--- a/src/selector.rs
+++ b/src/selector.rs
@@ -276,7 +276,9 @@ impl<'a> SelectorParser<'a> {
         }
         if let Some(Token { kind, .. }) = tokens.next() {
             match kind {
-                TokenKind::Ident(v) | TokenKind::Number(v) => self.selectors.push(SelectorKind::Element(v)),
+                TokenKind::Ident(v) | TokenKind::Number(v) => {
+                    self.selectors.push(SelectorKind::Element(v))
+                }
                 TokenKind::Symbol(Symbol::Period) => self.selectors.push(SelectorKind::Class),
                 TokenKind::Symbol(Symbol::Hash) => self.selectors.push(SelectorKind::Id),
                 TokenKind::Symbol(Symbol::Colon) => self.consume_pseudo_selector(tokens),
diff --git a/tests/color.rs b/tests/color.rs
index 3c9dc14..3255070 100644
--- a/tests/color.rs
+++ b/tests/color.rs
@@ -81,6 +81,18 @@ test!(
     opacity_function_number_unit,
     "a {\n  color: opacity(1px);\n}\n"
 );
+// blocked on better function-call argument parsing
+// specifically, passing lists as values
+// test!(
+//     rgba_one_arg,
+//     "a {\n  color: rgba(1 2 3);;\n}\n",
+//     "a {\n  color: #010203;\n}\n"
+// );
+test!(
+    rgba_two_args,
+    "a {\n  color: rgba(red, 0.5);\n}\n",
+    "a {\n  color: rgba(255, 0, 0, 0.5);\n}\n"
+);
 test!(
     rgba_opacity_over_1,
     "a {\n  color: rgba(1, 2, 3, 3);\n}\n",