diff --git a/src/components/expression/expressionButtons.js b/src/components/expression/expressionButtons.js
index e4109cf7..6ba48cc8 100644
--- a/src/components/expression/expressionButtons.js
+++ b/src/components/expression/expressionButtons.js
@@ -60,20 +60,37 @@ class Expression extends React.Component {
           eitherCellSetOneOrTwo={2}/>
         </div>
         <div>
-          <button
-            style={{
-              fontSize: 18,
-              margin: 10,
-              fontWeight: 700,
-              color: "#FFF",
-              padding: "12px 20px",
-              backgroundColor: globals.darkGreen,
-              border: "none",
-              cursor: "pointer",
-            }}
-            onClick={this.computeDiffExp.bind(this)}>
-            Compute differential expression
-          </button>
+          {
+            this.props.differential.celllist1 && this.props.differential.celllist2 ?
+            <button
+              style={{
+                fontSize: 18,
+                margin: 10,
+                fontWeight: 700,
+                color: "#FFF",
+                padding: "12px 20px",
+                backgroundColor: globals.brightBlue,
+                border: "none",
+                cursor: "pointer",
+              }}
+              onClick={this.computeDiffExp.bind(this)}>
+              Compute differential expression
+            </button> :
+            <button
+              style={{
+                fontSize: 18,
+                margin: 10,
+                fontWeight: 700,
+                color: "#FFF",
+                padding: "12px 20px",
+                backgroundColor: globals.mediumGrey,
+                border: "none",
+              }}
+              >
+              Compute differential expression
+            </button>
+          }
+
         </div>
       </div>
     )
diff --git a/src/components/graph/graph.js b/src/components/graph/graph.js
index 3afcc8fc..77cfb49b 100644
--- a/src/components/graph/graph.js
+++ b/src/components/graph/graph.js
@@ -242,7 +242,7 @@ class Graph extends React.Component {
               fontWeight: 400,
               color: "white",
               padding: "10px 20px",
-              backgroundColor: globals.darkGreen,
+              backgroundColor: globals.brightBlue,
               border: "none",
               cursor: "pointer",
             }}
diff --git a/src/globals.js b/src/globals.js
index 542b25bc..fffdf773 100644
--- a/src/globals.js
+++ b/src/globals.js
@@ -21,14 +21,15 @@ export const continuous = [
 ]
 
 /* colors */
-export const hcaBlue = "#1c7cc7"
+export const blue = "#4a90e2";
+export const hcaBlue = "#1c7cc7";
 export const lighterGrey = "rgb(245,245,245)";
 export const lightGrey = "rgb(211,211,211)";
 export const mediumGrey = "rgb(153,153,153)";
 export const darkGrey = "rgb(102,102,102)";
 export const darkerGrey = "rgb(51,51,51)";
 
-export const brightBlue = "#3B98FC";
+export const brightBlue = "#4a90e2";
 export const brightGreen = "#A2D729";
 export const darkGreen = "#448C4D";