fix

src/views/components/PenProps.vue

@@ -394,7 +394,6 @@
                         :color-modes="['monochrome']"
                         :enable-alpha="true"
                         :show-primary-color-preview="false"
-                        enable-alpha
                         v-model="data.pen.background"
                         @change="changeValue('background')"
                       />