diff --git a/src/visual/GratingStim.js b/src/visual/GratingStim.js
index dcf2c21..88015a0 100644
--- a/src/visual/GratingStim.js
+++ b/src/visual/GratingStim.js
@@ -40,7 +40,7 @@ import raisedCosShader from "./shaders/raisedCosShader.frag";
  * @param {String | HTMLImageElement} [options.mask] - the name of the mask resource or HTMLImageElement corresponding to the mask
  * @param {String} [options.units= "norm"] - the units of the stimulus (e.g. for size, position, vertices)
  * @param {number} [options.sf=1.0] - spatial frequency of the function used in grating stimulus
- * @param {number} [options.phase=1.0] - phase of the function used in grating stimulus
+ * @param {number} [options.phase=0.0] - phase of the function used in grating stimulus, multiples of period of that function
  * @param {Array.<number>} [options.pos= [0, 0]] - the position of the center of the stimulus
  * @param {number} [options.ori= 0.0] - the orientation (in degrees)
  * @param {number} [options.size] - the size of the rendered image (DEFAULT_STIM_SIZE_PX will be used if size is not specified)
@@ -142,7 +142,8 @@ export class GratingStim extends util.mix(VisualStim).with(ColorMixin)
 			shader: sinShader,
 			uniforms: {
 				uFreq: 1.0,
-				uPhase: 0.0
+				uPhase: 0.0,
+				uColor: [.5, 0, .5]
 			}
 		},
 		sqr: {
diff --git a/src/visual/shaders/sinShader.frag b/src/visual/shaders/sinShader.frag
index 5e53d87..441d2fd 100644
--- a/src/visual/shaders/sinShader.frag
+++ b/src/visual/shaders/sinShader.frag
@@ -18,9 +18,10 @@ out vec4 shaderOut;
 #define M_PI 3.14159265358979
 uniform float uFreq;
 uniform float uPhase;
+uniform vec3 uColor;
 
 void main() {
     vec2 uv = vUvs;
-    float s = sin(uFreq * uv.x * 2. * M_PI + uPhase);
-    shaderOut = vec4(.5 + .5 * vec3(s), 1.0);
+    float s = sin((uFreq * uv.x + uPhase) * 2. * M_PI);
+    shaderOut = vec4((.5 + .5 * vec3(s)) * uColor, 1.0);
 }
diff --git a/src/visual/shaders/sinXsinShader.frag b/src/visual/shaders/sinXsinShader.frag
index 9b8ffda..21d3975 100644
--- a/src/visual/shaders/sinXsinShader.frag
+++ b/src/visual/shaders/sinXsinShader.frag
@@ -16,13 +16,14 @@ in vec2 vUvs;
 out vec4 shaderOut;
 
 #define M_PI 3.14159265358979
+#define PI2 2.* M_PI
 uniform float uFreq;
 uniform float uPhase;
 
 void main() {
     vec2 uv = vUvs;
-    float sx = sin(uFreq * uv.x * 2. * M_PI + uPhase);
-    float sy = sin(uFreq * uv.y * 2. * M_PI + uPhase);
+    float sx = sin((uFreq * uv.x + uPhase) * PI2);
+    float sy = sin((uFreq * uv.y + uPhase) * PI2);
     float s = sx * sy * .5 + .5;
     shaderOut = vec4(vec3(s), 1.0);
 }
diff --git a/src/visual/shaders/sqrShader.frag b/src/visual/shaders/sqrShader.frag
index 1d69602..f44ffca 100644
--- a/src/visual/shaders/sqrShader.frag
+++ b/src/visual/shaders/sqrShader.frag
@@ -21,6 +21,6 @@ uniform float uPhase;
 
 void main() {
     vec2 uv = vUvs;
-    float s = sign(sin(uFreq * uv.x * 2. * M_PI + uPhase));
+    float s = sign(sin((uFreq * uv.x + uPhase) * 2. * M_PI));
     shaderOut = vec4(.5 + .5 * vec3(s), 1.0);
 }
diff --git a/src/visual/shaders/sqrXsqrShader.frag b/src/visual/shaders/sqrXsqrShader.frag
index 4f320ab..6f140b4 100644
--- a/src/visual/shaders/sqrXsqrShader.frag
+++ b/src/visual/shaders/sqrXsqrShader.frag
@@ -16,13 +16,14 @@ in vec2 vUvs;
 out vec4 shaderOut;
 
 #define M_PI 3.14159265358979
+#define PI2 2.* M_PI
 uniform float uFreq;
 uniform float uPhase;
 
 void main() {
     vec2 uv = vUvs;
-    float sx = sign(sin(uFreq * uv.x * 2. * M_PI + uPhase));
-    float sy = sign(sin(uFreq * uv.y * 2. * M_PI + uPhase));
+    float sx = sign(sin((uFreq * uv.x + uPhase) * PI2));
+    float sy = sign(sin((uFreq * uv.y + uPhase) * PI2));
     float s = sx * sy * .5 + .5;
     shaderOut = vec4(vec3(s), 1.0);
 }