diff --git a/src/flow.js b/src/flow.js
index 5ad372f..de10db9 100644
--- a/src/flow.js
+++ b/src/flow.js
@@ -38,13 +38,13 @@ function setStyle(ctx, {x, x2, options}) {
   let fill;
 
   if (options.colorMode === 'from') {
-    fill = color(options.colorFrom).alpha(0.5).rgbString();
+    fill = color(options.colorFrom).alpha(options.alpha).rgbString();
   } else if (options.colorMode === 'to') {
-    fill = color(options.colorTo).alpha(0.5).rgbString();
+    fill = color(options.colorTo).alpha(options.alpha).rgbString();
   } else {
     fill = ctx.createLinearGradient(x, 0, x2, 0);
-    fill.addColorStop(0, color(options.colorFrom).alpha(0.5).rgbString());
-    fill.addColorStop(1, color(options.colorTo).alpha(0.5).rgbString());
+    fill.addColorStop(0, color(options.colorFrom).alpha(options.alpha).rgbString());
+    fill.addColorStop(1, color(options.colorTo).alpha(options.alpha).rgbString());
   }
 
   ctx.fillStyle = fill;
@@ -182,6 +182,7 @@ Flow.defaults = {
   colorFrom: 'red',
   colorTo: 'green',
   colorMode: 'gradient',
+  alpha: 0.5,
   hoverColorFrom: (ctx, options) => getHoverColor(options.colorFrom),
   hoverColorTo: (ctx, options) => getHoverColor(options.colorTo)
 };