diff --git a/random-walkers.js b/random-walkers.js
index b91039e..4d8d49f 100644
--- a/random-walkers.js
+++ b/random-walkers.js
@@ -16,7 +16,7 @@ window.onload = function() {
     autoPlace: false,
   });
 
-  gui.add(controls, "step_time", 200, 2000).name("step time ms").step(1);
+  gui.add(controls, "step_time", 50, 1000).name("step time ms").step(50);
   gui.add(controls, "fadeout", 0, 20).name("trail fadeout length (0 to disable)").step(1);
   //gui.add(controls, "cell_size", 10, 100).name("cell size").step(1);
   gui.addColor(controls, "color").name("guy color");
@@ -27,7 +27,7 @@ window.onload = function() {
 };
 
 var controls = new(function() {
-  this.step_time = 500;
+  this.step_time = 200;
   this.fadeout = 10;
   this.cell_size = 22;
   this.color = "#FFB000";
@@ -92,7 +92,11 @@ function init_walk() {
 }
 
 function move_walker() {
-  add_random_direction(walker_pos);
+  // leave a trail
+  trails.push({row: walker.row, col: walker.col, color: walker.color});
+
+  // move in random dir
+  add_random_direction(walker);
 }
 
 function add_random_direction(pos) {
@@ -116,6 +120,26 @@ function add_random_direction(pos) {
  * Drawing                                                                  *
  ****************************************************************************/
 
+// from https://www.sitepoint.com/javascript-generate-lighter-darker-color/
+function tweak_color_luminance(hex, lum) {
+  // validate hex string
+  hex = String(hex).replace(/[^0-9a-f]/gi, '');
+  if (hex.length < 6) {
+    hex = hex[0]+hex[0]+hex[1]+hex[1]+hex[2]+hex[2];
+  }
+  lum = lum || 0;
+
+  // convert to decimal and change luminosity
+  var rgb = "#", c, i;
+  for (i = 0; i < 3; i++) {
+    c = parseInt(hex.substr(i*2,2), 16);
+    c = Math.round(Math.min(Math.max(0, c + (c * lum)), 255)).toString(16);
+    rgb += ("00"+c).substr(c.length);
+  }
+
+  return rgb;
+}
+
 function draw() {
   // pixel width and height
   var old_width = ctx.canvas.width;
@@ -143,7 +167,13 @@ function draw() {
   draw_grid();
 
   // draw a colored square at the walker location
-  draw_grid_square(walker_pos.row, walker_pos.col, "red");
+  draw_grid_square(walker.row, walker.col, walker.color);
+
+  // for any trails, draw them
+  for (var i = 0; i < trails.length; i++) {
+    t = trails[i];
+    draw_grid_square(t.row, t.col, t.color);
+  }
 
   // TODO CODE
 }
@@ -186,5 +216,6 @@ var offset_v = (canvas.height - (controls.cell_size * n_rows)).div(2);
 var offset = {h: offset_h, v: offset_v};
 
 // set start position of walker and start the random walk
-var walker_pos = {row: n_rows.div(2), col: n_cols.div(2)};
+var walker = {row: n_rows.div(2), col: n_cols.div(2), color: controls.color};
+trails = []
 init_walk();