If you like blue,try this backend theme
Manon: A clean elegant user interface designed for Odoo administrative interface.
One of the best backend theme available for Odoo with extensive change in look & feel
Customised POS Interface, Works with and without Restaurant module.
Accordion Menu, Font Awesome Icon
Odoo Backend Theme v11
Transparent Backend Theme v11.0
Fully responsive Uppercrust Backend Theme(Without Global Search) is available in v9, v10, v11, v12. Kindly contact us to buy it in various versions
Odoo 11.0 community backend theme