bl_info = {
    "name": "Active Background",
    "author": "Dspazio",
    "version": (1, 0),
    "blender": (2, 80, 0),
    "location": "View3D",
    "description": "Changes background gradient color for each mode.",
    "warning": "",
    "doc_url": "",
    "category": "Themes",
}

import bpy
from bpy.app.handlers import persistent

Modes = {'OBJECT':(0.30, 0.30, 0.30),
#			ORIG
#			 'EDIT':(0.30, 0.20, 0.20),
#			xxxx
          'EDIT':(0.50, 0.20, 0.20),
#			-------------------------------
#			ORIG
#        'SCULPT':(0.05, 0.05, 0.05),
#			Blue1
#       'SCULPT':(0.1, 0.5, 0.6),
#			Pink1
#			'SCULPT':(0.8, 0.5, 0.6),
#			Turquoise
#			'SCULPT':(0.0, 0.4, 0.4),
#			RoyaleBlue
			'SCULPT':(0.0, 0.1, 0.6),
#			-------------------------------
        'VERTEX_PAINT':(0.05, 0.05, 0.05),
        'WEIGHT_PAINT':(0.05, 0.05, 0.05),
        'TEXTURE_PAINT':(0.05, 0.05, 0.05)}

@persistent
def my_handler(scene):
    mode = bpy.context.object.mode
    bpy.context.preferences.themes[0].view_3d.space.gradients.high_gradient = Modes[mode]
    
class addActiveBackgroundPreferences(bpy.types.AddonPreferences):
      bl_idname = __name__
 
      edit_mode_color: bpy.props.FloatVectorProperty(name="Edit Mode Color", subtype='COLOR', default=Modes['EDIT'], size=3, min=0, max=1)
        
      def draw(self, context):
          layout = self.layout
          layout.label(text='Edit Mode :')
          row = layout.row()
          row.prop(self, 'edit_mode_color', expand=True)
    
def register():
    bpy.app.handlers.depsgraph_update_post.append(my_handler)
    bpy.utils.register_class(addActiveBackgroundPreferences)

def unregister():
    bpy.app.handlers.depsgraph_update_post.remove(my_handler)
    bpy.utils.register_class(addActiveBackgroundPreferences)

if __name__ == "__main__":
    register()