org-agenda-with-colors in block agenda

Hi all,

For printing custom agenda commands, I like to set the local option
org-agenda-with-colors to nil.

This works fine for single agenda commands, such as 

(setq org-agenda-custom-commands
      '(("o" "Office" tags-todo "office"
	 ((org-agenda-with-colors nil)))))

But I cannot get it to work with block agendas. For instance, the
following results in an agenda view with colors:

(setq org-agenda-custom-commands
      '(("g" "GTD Contexts"
	 ((tags-todo "office")
	  (tags-todo "computer")
	  (tags-todo "phone")
	  (tags-todo "errands"))
	 ((org-agenda-with-colors nil)))))

The same behavior results if I add the option to each separate element
of the block agenda.

Is this perhaps a bug? I'm using org 6.17 in emacs 22. Any advice
would be greatly appreciated.

Thanks,