增加尚未选择颜色的提示。

src/components/FloatColorPicker.module.css

@@ -14,6 +14,10 @@
         border-radius: var(--border-radius-xxs);
         border: 1px solid var(--color-border);
         cursor: pointer;
+        display: flex;
+        justify-content: center;
+        align-items: center;
+        font-size: var(--font-size-xs);
       }
     }
     .picker {

src/components/FloatColorPicker.tsx

@@ -35,7 +35,9 @@ export function FloatColorPicker({ name, color, onPick }: FloatColorPickerProps)
           onClick={() => setPickerShow(true)}
           style={{
             backgroundColor: isNil(pickedColor) ? 'rgba(0, 0, 0, 0)' : `#${pickedColor}`,
-          }}></div>
+          }}>
+          {isNil(pickedColor) && <span>N/A</span>}
+        </div>
         <ActionIcon icon="tabler:x" onClick={() => handlePickAction(null)} />
       </div>
       {showPicker && (