Refactor color management and UI components for consistency

- Updated color references in various widgets to use the new `opaquePrimary` color for better visual consistency.
- Refactored `ColorsManager` to improve color definitions and removed redundant color declarations.
- Enhanced UI elements across multiple dialogs and widgets to ensure a cohesive design language.

This change promotes maintainability and aligns with the updated color scheme.

lib/common/dialog_dropdown.dart

@@ -66,7 +66,7 @@ class _DialogDropdownState extends State<DialogDropdown> {
                 child: Material(
                   elevation: 4.0,
                   child: Container(
-                    color: ColorsManager.whiteColors,
+                    color: ColorsManager.white,
                     constraints: const BoxConstraints(
                       maxHeight: 200.0, // Set max height for dropdown
                     ),
@@ -87,12 +87,10 @@ class _DialogDropdownState extends State<DialogDropdown> {
                           child: ListTile(
                             title: Text(
                               item,
-                              style: Theme.of(context)
-                                  .textTheme
-                                  .bodyMedium
-                                  ?.copyWith(
-                                    color: ColorsManager.textPrimaryColor,
-                                  ),
+                              style:
+                                  Theme.of(context).textTheme.bodyMedium?.copyWith(
+                                        color: ColorsManager.textPrimaryColor,
+                                      ),
                             ),
                             onTap: () {
                               widget.onSelected(item);