I cant put color on the buttons of the header I have this codeto the header:

<header>

   <button name="pet_regist" string="registado" status="registado"  class="oe_highlight" type="workflow" />
   <field name="state" widget="statusbar" statusbar_visible="novo,registado,validado,morto" 
     statusbar_colors='{"novo":"blue","registado":"blue","validado":"blue","morto":"blue"}' /> 
</header>

my buttons of the header on the right are grey I need in first instance when I click on the create button the "novo" shows in blue.