Is there anyway to change the property input background color to red?

Question

I'm creating an Add-on where you have to select any object type to start using it. but I would like to know if is there any way to display a red property input if no object is selected or exists.

• This image is an screenshot of driver editor pop-up

Answer 1

Yes. Just set Layout.alert property to True in case there is no object selected:

Demo based on @batFINGERs answer to Object selection box with eyedropper.

import bpy
from bpy.props import PointerProperty


class TEST_PT_layout_panel(bpy.types.Panel):
    bl_label = "Prop Panels"
    bl_category = "Test Panel"
    bl_space_type = 'PROPERTIES'
    bl_region_type = 'WINDOW'
    bl_context = "scene"

    def draw(self, context):
        scene = context.scene
        layout = self.layout
        
        col = layout.column()
        if not scene.prop:
            col.alert = True
        else:
            col.alert = False
            
        col.prop(scene, "prop")


def register():
    bpy.types.Scene.prop = PointerProperty(type=bpy.types.Object)
    bpy.utils.register_class(TEST_PT_layout_panel)


def unregister():
    bpy.utils.unregister_class(TEST_PT_layout_panel)
    
if __name__ == "__main__":
    register()