fix(VBtn): don't add color classes when disabled

fixes #8030

packages/vuetify/src/components/VBtn/VBtn.ts

@@ -189,6 +189,6 @@ export default baseMixins.extend<options>().extend({
       ? this.value
       : JSON.stringify(this.value)
 
-    return h(tag, setColor(this.color, data), children)
+    return h(tag, this.disabled ? data : setColor(this.color, data), children)
   },
 })

packages/vuetify/src/components/VBtn/__tests__/VBtn.spec.ts

@@ -270,4 +270,19 @@ describe('VBtn.ts', () => {
     wrapper.setProps({ value: { foo: 'bar' } })
     expect(wrapper.attributes('value')).toBe('{"foo":"bar"}')
   })
+
+  it('should not add color classes if disabled', () => {
+    const wrapper = mountFunction({
+      propsData: {
+        color: 'primary--text text--darken-2',
+      },
+    })
+
+    expect(wrapper.html()).toMatchSnapshot()
+
+    wrapper.setProps({
+      disabled: true,
+    })
+    expect(wrapper.html()).toMatchSnapshot()
+  })
 })

packages/vuetify/src/components/VBtn/__tests__/__snapshots__/VBtn.spec.ts.snap

@@ -1,5 +1,24 @@
 // Jest Snapshot v1, https://goo.gl/fbAQLP
 
+exports[`VBtn.ts should not add color classes if disabled 1`] = `
+<button type="button"
+        class="v-btn v-btn--contained theme--light v-size--default primary--text text--darken-2"
+>
+  <span class="v-btn__content">
+  </span>
+</button>
+`;
+
+exports[`VBtn.ts should not add color classes if disabled 2`] = `
+<button type="button"
+        class="v-btn v-btn--contained v-btn--disabled theme--light v-size--default"
+        disabled="disabled"
+>
+  <span class="v-btn__content">
+  </span>
+</button>
+`;
+
 exports[`VBtn.ts should render an <a> tag when using href prop 1`] = `
 <a href="http://www.google.com"
    class="v-btn v-btn--contained theme--light v-size--default"