diff --git a/cmd/vitals/main.go b/cmd/vitals/main.go
index 39f87f6..8ff0636 100644
--- a/cmd/vitals/main.go
+++ b/cmd/vitals/main.go
@@ -22,7 +22,6 @@ import (
 	"github.com/Jason-Adam/vitals/internal/preset"
 	"github.com/Jason-Adam/vitals/internal/render"
 	"github.com/Jason-Adam/vitals/internal/stdin"
-	"github.com/lucasb-eyer/go-colorful"
 )
 
 // installPath is the go install target for the update command.
@@ -408,13 +407,15 @@ func queryLightBackground() (light bool, ok bool) {
 }
 
 // isLightColor returns true when a color's HSL lightness is >= 0.5.
-// Mirrors lipgloss's unexported isDarkColor with the inverse condition.
+// Uses the standard RGB-to-HSL lightness formula: L = (max + min) / 2.
 func isLightColor(c color.Color) bool {
-	col, ok := colorful.MakeColor(c)
-	if !ok {
-		return false // can't determine — assume dark (safe default)
-	}
-	_, _, l := col.Hsl()
+	r, g, b, _ := c.RGBA()
+	rf := float64(r) / 0xffff
+	gf := float64(g) / 0xffff
+	bf := float64(b) / 0xffff
+	mx := max(rf, gf, bf)
+	mn := min(rf, gf, bf)
+	l := (mx + mn) / 2
 	return l >= 0.5
 }
 
diff --git a/cmd/vitals/main_test.go b/cmd/vitals/main_test.go
index 2a47abf..090104a 100644
--- a/cmd/vitals/main_test.go
+++ b/cmd/vitals/main_test.go
@@ -2,6 +2,7 @@ package main
 
 import (
 	"bytes"
+	"image/color"
 	"os"
 	"path/filepath"
 	"strings"
@@ -260,6 +261,30 @@ func TestWatchAndRender_DetectsFileChange(t *testing.T) {
 	}
 }
 
+func TestIsLightColor(t *testing.T) {
+	tests := []struct {
+		name string
+		c    color.Color
+		want bool
+	}{
+		{"black", color.Black, false},
+		{"white", color.White, true},
+		{"dark gray", color.RGBA{R: 64, G: 64, B: 64, A: 255}, false},
+		{"light gray", color.RGBA{R: 192, G: 192, B: 192, A: 255}, true},
+		{"mid gray below threshold", color.RGBA{R: 126, G: 126, B: 126, A: 255}, false},
+		{"mid gray at threshold", color.RGBA{R: 128, G: 128, B: 128, A: 255}, true},
+		{"pure red", color.RGBA{R: 255, G: 0, B: 0, A: 255}, true},
+		{"dark blue", color.RGBA{R: 0, G: 0, B: 128, A: 255}, false},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			if got := isLightColor(tt.c); got != tt.want {
+				t.Errorf("isLightColor(%v) = %v, want %v", tt.c, got, tt.want)
+			}
+		})
+	}
+}
+
 func TestFindCurrentTranscript_ReturnsNewest(t *testing.T) {
 	tmp := t.TempDir()
 	t.Setenv("HOME", tmp)
diff --git a/go.mod b/go.mod
index 25a5882..48b9c43 100644
--- a/go.mod
+++ b/go.mod
@@ -7,16 +7,16 @@ require (
 	github.com/BurntSushi/toml v1.6.0
 	github.com/charmbracelet/colorprofile v0.4.2
 	github.com/charmbracelet/x/ansi v0.11.6
-	github.com/charmbracelet/x/term v0.2.2
-	github.com/lucasb-eyer/go-colorful v1.3.0
 )
 
 require (
 	github.com/charmbracelet/ultraviolet v0.0.0-20251205161215-1948445e3318 // indirect
+	github.com/charmbracelet/x/term v0.2.2 // indirect
 	github.com/charmbracelet/x/termios v0.1.1 // indirect
 	github.com/charmbracelet/x/windows v0.2.2 // indirect
 	github.com/clipperhouse/displaywidth v0.11.0 // indirect
 	github.com/clipperhouse/uax29/v2 v2.7.0 // indirect
+	github.com/lucasb-eyer/go-colorful v1.3.0 // indirect
 	github.com/mattn/go-runewidth v0.0.21 // indirect
 	github.com/muesli/cancelreader v0.2.2 // indirect
 	github.com/rivo/uniseg v0.4.7 // indirect
diff --git a/internal/gather/gather.go b/internal/gather/gather.go
index 7ed9736..8948df8 100644
--- a/internal/gather/gather.go
+++ b/internal/gather/gather.go
@@ -19,7 +19,6 @@ import (
 	"github.com/Jason-Adam/vitals/internal/git"
 	"github.com/Jason-Adam/vitals/internal/model"
 	"github.com/Jason-Adam/vitals/internal/transcript"
-	"github.com/charmbracelet/x/term"
 )
 
 // transcriptWidgets are the widget names that require transcript data.
@@ -265,7 +264,7 @@ func sessionStart(path string) string {
 // (defaultTerminalWidth) when this returns 0.
 func terminalWidth() int {
 	for _, fd := range []uintptr{os.Stdin.Fd(), os.Stderr.Fd(), os.Stdout.Fd()} {
-		if w, _, err := term.GetSize(fd); err == nil && w > 0 {
+		if w := getTermWidth(fd); w > 0 {
 			return w
 		}
 	}
diff --git a/internal/gather/termsize_other.go b/internal/gather/termsize_other.go
new file mode 100644
index 0000000..22547e6
--- /dev/null
+++ b/internal/gather/termsize_other.go
@@ -0,0 +1,7 @@
+//go:build !unix
+
+package gather
+
+// getTermWidth is a no-op on non-Unix platforms; the caller falls back
+// to the COLUMNS env var.
+func getTermWidth(_ uintptr) int { return 0 }
diff --git a/internal/gather/termsize_unix.go b/internal/gather/termsize_unix.go
new file mode 100644
index 0000000..f9693db
--- /dev/null
+++ b/internal/gather/termsize_unix.go
@@ -0,0 +1,26 @@
+//go:build unix
+
+package gather
+
+import (
+	"syscall"
+	"unsafe"
+)
+
+// getTermWidth returns the terminal width for the given file descriptor
+// via the TIOCGWINSZ ioctl, or 0 if the fd is not a terminal.
+func getTermWidth(fd uintptr) int {
+	var ws struct {
+		Row, Col       uint16
+		Xpixel, Ypixel uint16
+	}
+	_, _, err := syscall.Syscall(
+		syscall.SYS_IOCTL, fd,
+		syscall.TIOCGWINSZ,
+		uintptr(unsafe.Pointer(&ws)),
+	)
+	if err != 0 || ws.Col == 0 {
+		return 0
+	}
+	return int(ws.Col)
+}