diff --git a/Gemfile b/Gemfile
index 86413b01..53a6d1e5 100644
--- a/Gemfile
+++ b/Gemfile
@@ -13,7 +13,8 @@ group :test do
   gem "rspec", ">= 3.2"
   gem "rspec-mocks", ">= 3"
   gem "simplecov", ">= 0.13"
-  gem "webmock"
+  gem "webmock", '~> 3.14.0' if Gem::Version.new(RUBY_VERSION) < Gem::Version.new("2.4.0")
+  gem "webmock", '>= 3.14' if Gem::Version.new(RUBY_VERSION) >= Gem::Version.new("2.4.0")
 end
 
 gemspec
diff --git a/lib/thor/shell/color.rb b/lib/thor/shell/color.rb
index 33e9d9d9..aee95292 100644
--- a/lib/thor/shell/color.rb
+++ b/lib/thor/shell/color.rb
@@ -105,7 +105,7 @@ def are_colors_supported?
       end
 
       def are_colors_disabled?
-        !ENV['NO_COLOR'].nil?
+        !ENV['NO_COLOR'].nil? && !ENV['NO_COLOR'].empty?
       end
 
       # Overwrite show_diff to show diff with colors if Diff::LCS is
diff --git a/spec/shell/color_spec.rb b/spec/shell/color_spec.rb
index a0f9686a..2c63bee7 100644
--- a/spec/shell/color_spec.rb
+++ b/spec/shell/color_spec.rb
@@ -21,8 +21,8 @@ def shell
       shell.ask "Is this green?", :green, :limited_to => %w(Yes No Maybe)
     end
 
-    it "does not set the color if specified and NO_COLOR is set" do
-      allow(ENV).to receive(:[]).with("NO_COLOR").and_return("")
+    it "does not set the color if specified and NO_COLOR is set to a non-empty value" do
+      allow(ENV).to receive(:[]).with("NO_COLOR").and_return("non-empty value")
       expect(Thor::LineEditor).to receive(:readline).with("Is this green? ", anything).and_return("yes")
       shell.ask "Is this green?", :green
 
@@ -30,6 +30,24 @@ def shell
       shell.ask "Is this green?", :green, :limited_to => %w(Yes No Maybe)
     end
 
+    it "sets the color when NO_COLOR is ignored because the environment variable is nil" do
+      allow(ENV).to receive(:[]).with("NO_COLOR").and_return(nil)
+      expect(Thor::LineEditor).to receive(:readline).with("\e[32mIs this green? \e[0m", anything).and_return("yes")
+      shell.ask "Is this green?", :green
+
+      expect(Thor::LineEditor).to receive(:readline).with("\e[32mIs this green? [Yes, No, Maybe] \e[0m", anything).and_return("Yes")
+      shell.ask "Is this green?", :green, :limited_to => %w(Yes No Maybe)
+    end
+
+    it "sets the color when NO_COLOR is ignored because the environment variable is an empty-string" do
+      allow(ENV).to receive(:[]).with("NO_COLOR").and_return("")
+      expect(Thor::LineEditor).to receive(:readline).with("\e[32mIs this green? \e[0m", anything).and_return("yes")
+      shell.ask "Is this green?", :green
+
+      expect(Thor::LineEditor).to receive(:readline).with("\e[32mIs this green? [Yes, No, Maybe] \e[0m", anything).and_return("Yes")
+      shell.ask "Is this green?", :green, :limited_to => %w(Yes No Maybe)
+    end
+
     it "handles an Array of colors" do
       expect(Thor::LineEditor).to receive(:readline).with("\e[32m\e[47m\e[1mIs this green on white? \e[0m", anything).and_return("yes")
       shell.ask "Is this green on white?", [:green, :on_white, :bold]
@@ -59,13 +77,31 @@ def shell
       expect(out.chomp).to eq("Wow! Now we have colors!")
     end
 
-    it "does not set the color if NO_COLOR is set" do
+    it "does not set the color if NO_COLOR is set to any value that is not an empty string" do
+      allow(ENV).to receive(:[]).with("NO_COLOR").and_return("non-empty string value")
+      out = capture(:stdout) do
+        shell.say "NO_COLOR is enforced! We should not have colors!", :green
+      end
+
+      expect(out.chomp).to eq("NO_COLOR is enforced! We should not have colors!")
+    end
+
+    it "colors are still used and NO_COLOR is ignored if the environment variable is nil" do
+      allow(ENV).to receive(:[]).with("NO_COLOR").and_return(nil)
+      out = capture(:stdout) do
+        shell.say "NO_COLOR is ignored! We have colors!", :green
+      end
+
+      expect(out.chomp).to eq("\e[32mNO_COLOR is ignored! We have colors!\e[0m")
+    end
+
+    it "colors are still used and NO_COLOR is ignored if the environment variable is an empty-string" do
       allow(ENV).to receive(:[]).with("NO_COLOR").and_return("")
       out = capture(:stdout) do
-        shell.say "Wow! Now we have colors!", :green
+        shell.say "NO_COLOR is ignored! We have colors!", :green
       end
 
-      expect(out.chomp).to eq("Wow! Now we have colors!")
+      expect(out.chomp).to eq("\e[32mNO_COLOR is ignored! We have colors!\e[0m")
     end
 
     it "does not use a new line even with colors" do
@@ -145,12 +181,34 @@ def shell
       expect(colorless).to eq("hi!")
     end
 
-    it "does nothing when the NO_COLOR environment variable is set" do
-      allow(ENV).to receive(:[]).with("NO_COLOR").and_return("")
+    it "does nothing when the NO_COLOR environment variable is set to a non-empty string" do
+      allow(ENV).to receive(:[]).with("NO_COLOR").and_return("non-empty value")
       allow($stdout).to receive(:tty?).and_return(true)
       colorless = shell.set_color "hi!", :white
       expect(colorless).to eq("hi!")
     end
+
+    it "sets color when the NO_COLOR environment variable is ignored for being nil" do
+      allow(ENV).to receive(:[]).with("NO_COLOR").and_return(nil)
+      allow($stdout).to receive(:tty?).and_return(true)
+
+      red = shell.set_color "hi!", :red
+      expect(red).to eq("\e[31mhi!\e[0m")
+
+      on_red = shell.set_color "hi!", :white, :on_red
+      expect(on_red).to eq("\e[37m\e[41mhi!\e[0m")
+    end
+
+    it "sets color when the NO_COLOR environment variable is ignored for being an empty string" do
+      allow(ENV).to receive(:[]).with("NO_COLOR").and_return("")
+      allow($stdout).to receive(:tty?).and_return(true)
+
+      red = shell.set_color "hi!", :red
+      expect(red).to eq("\e[31mhi!\e[0m")
+
+      on_red = shell.set_color "hi!", :white, :on_red
+      expect(on_red).to eq("\e[37m\e[41mhi!\e[0m")
+    end
   end
 
   describe "#file_collision" do