Examples: Avoid using ImColor() to not tempt newcomers into looking at it

examples/vulkan_example/main.cpp

@@ -664,7 +664,7 @@ int main(int, char**)
 
     bool show_test_window = true;
     bool show_another_window = false;
-    ImVec4 clear_color = ImColor(114, 144, 154);
+    ImVec4 clear_color = ImVec4(0.45f, 0.55f, 0.60f, 1.00f);
 
     // When IMGUI_UNLIMITED_FRAME_RATE is defined we render into latest image acquired from the swapchain but we display the image which was rendered before.
     // Hence we must render once and increase the g_FrameIndex without presenting, which we do before entering the render loop.